NEW YORK — Broadway slowed a bit in Week 21 (Oct. 13-19), the week after its Columbus Day weekend spike, with most shows slipping at the box office.A handful of productions managed to buck the downward trend, including “Gypsy” ($742,890), which posted the highest gain of the frame at $67,000 more than the prior sesh. “The Seagull” ($521,033) and “Boeing-Boeing” ($406,477) were among the shows to register solid five-figure gains, as did “Speed-the-Plow” ($367,137), despite the fact that comp-heavy press perfs began last weekend. Meanwhile, “August: Osage County” ($472,334) rose by $20,000 and previewing tuner “Billy Elliot” ($731,471) climbed slightly in a five-perf week (originally skedded to be six perfs until a tech malfunction scuttled one show). For the most part, however, individual productions followed the Street, dipping about $600,000 to around $18 million for 29 shows on the boards (or $18.6 million including estimates for “Young Frankenstein”). Often the most volatile of the Disney musicals, “Mary Poppins” (off $70,000 to $693,835) saw the steepest decline. “Monty Python’s Spamalot” ($498,146), “Grease” ($485,689) and “Spring Awakening” ($347,393), among others, experienced drops in the $50,000 range. Of the tuners to open this fall, “A Tale of Two Cities” ($413,877) sagged only slightly, but “13″ ($228,201) slid more than $40,000. Total attendance was off about 7,000 from the prior frame and about 3,500 from the same week last year — the first time since economic fears became the talk of the town that attendance has lagged the previous year’s weekly total. (Sales tally, however, remained ahead by about $600,000.) The one show to close last week, “Legally Blonde” ($655,663), fell slightly in its final frame on the Rialto, playing to 85% capacity auds. The 21 musicals grossed $14,247,143 for 79.3% of the Broadway total, with an attendance of 177,195 at 81.7% capacity and average paid admission of $80.40. The nine plays grossed $3,717,279 for 20.7% of the Broadway total, with an attendance of 49,649 at 85.4% capacity and average paid admission of $74.87. Average paid admission was $79.19 for all shows.