21685

Appears in sequences

• Floor[n(n-1)(n-2)(n-3)/14].at n=25A011924
• Denominators of continued fraction convergents to sqrt(421).at n=12A041801
• Numerators of continued fraction convergents to sqrt(610).at n=6A042170
• Numerators of continued fraction convergents to sqrt(767).at n=10A042478
• Minimal positive solution x of Pell equation y^2 - A077426(n)*x^2 = -4.at n=47A078357
• Main diagonal of square table A086623 of coefficients of f(x,y) that satisfies f(x,y) = (1-xy)/[(1-x)(1-y)] + xy*f(x,y)^2.at n=7A086624
• a(n) = Sum_{k=0..n} C(n-k, floor(k/2))*3^k.at n=11A097335
• Twice the coefficient of sqrt(q) in e^h, where e is the fundamental unit and h is the class number of Q(sqrt(q)), q prime and congruent to 1 mod 4. (The coefficient lies in (1/2)Z, so twice it is an integer.)at n=39A225432
• Irregular triangle of numerators of the average value of the first letter over all derangements of {1, 2, ..., n} with k descents.at n=30A332009
• G.f. A(x) satisfies: A(x) = x + x^2 * exp( Sum_{k>=1} (-1)^(k+1) * A(x^k)^2 / k ).at n=19A363386