Focus groups can be the death of any aspiring series. For “Numbers,” a show that wore advanced mathematics on its sleeve, you might as well have given husband-and-wife co-creators Nick Falacci and Cheryl Heuton a blindfold and cigarette.

But a funny thing happened when “Numbers” walked the plank.

“When they asked the focus groups, ‘In one word, why do you like this show?’ they all said, ‘The math,'” Falacci says.

“Only then did we know this premise works,” Heuton adds. “We kind of reinvented Sherlock Holmes with algorithms,” Falacci quips.

American society might be dumbing down, but in reaching 100 episodes, “Numbers,” starring David Krumholtz as math whiz Charlie Eppes, has shown that smarts can measure up.

“There was such an enthusiastic response to the concept,” CBS Entertainment president Nina Tassler recalls. “People said, ‘Oh my God, I love the concept. I love the idea for a series. It’s a unique way of telling stories. We love Charlie.’ David Krumholtz was in the original cast. But we had some work to do. We recast, reshot and went right to series.”

The end result was gratifying for Falacci and Heuton, who knew that their show about a mathematician “was going to be a tough sell to a major network,” Heuton says. Long fascinated with mathematicians, scientists and physicists, they wanted to write about math and how mathematicians think, but needed a killer concept to draw viewers.

“This was in 2003,” Heuton says. “‘CSI’ by then was a massive, game-changing hit for CBS. So we thought using math as a tool to solve crimes would be something networks would understand. That’s how it became a crime-solving show.”

Says Tassler: “When Nick and Cheryl pitched the show, they were very specific on the characters. Our procedurals do very well, and they gave us incredibly detailed analysis of how authentic this approach is — that it’s a technique used in real case-solving.”

Scott Free Prods. got involved with the pilot, even though brothers Tony and Ridley Scott — executive producers of the show — had doubts.

“To be honest, we were really worried about it,” Tony Scott says. “It’s a very dangerous premise: Here’s a show about solving crime through mathematics.”

Audiences don’t question TV doctors spouting medical lingo, but would they so benignly accept complex equations? Scott knew they’d have to make the math accessible to the audience.

“We had to see if we could find a common denominator or some kind of throughline,” he says, “so we could take (Charlie’s) anecdotes and apply them to different stories and situations.

“I want the audience to work for their information, but if they work too hard, they’re going to switch off. It’s a fine balance,” Scott adds. “Our audience stays engaged because it’s at a level where they can jigsaw, they can put the pieces together. They can do the subtractions and the additions, and they like that sort of engagement.”

Creating the right balance of math, crime and characters was also crucial.

“American audiences like crime procedurals,” Heuton says, “particularly if there’s a good dose of character and humor to them.” So they added a family component to the story.

Tassler liked that. “It was about an older brother who had to overcompensate for having a prodigious younger brother, and how it affected the dynamic of their relationship, not only with each other, but with their parents, their father,” she says.

Naysayers still abounded, saying a TV series couldn’t cover three separate worlds — the FBI, the university and home. Heuton and Falacci disagreed, believing that blending the realms would help show the cases’ impact on the brothers and their co-workers.

“With an FBI agent in one world and a college professor in another, you want to see where they meet in the middle,” Heuton says.

One challenge remained for “Numbers”: its Friday airdate.

“It’s a tough night to pull an audience because there’s probably 25 to 30 million fewer sets on,” Heuton says. “We’re the little show you have to know about.”

Tassler says CBS has no plans to change the timeslot for ‘Numbers.”

“The show does really well where it is,” she says, “and it has such a loyal fanbase. I think they like watching it on Friday nights — which is why the show does so well — and we really don’t want to upset the applecart.”