291720

Appears in sequences

• a(n) = (2*n+3)!/(6*n!*(n+1)!).at n=7A002802
• Triangle read by rows giving number of ways to glue sides of a 2n-gon so as to produce a surface of genus g.at n=26A035309
• Array T(i,j) = binomial(-1/2-i,j)*(-4)^j, i,j >= 0 read by antidiagonals going down.at n=47A046521
• Number of symmetric nonnegative integer 8 X 8 matrices with sum of elements equal to 4*n, under action of dihedral group D_4.at n=19A054498
• Number of ways to use the elements of {1,...,k}, 0 <= k <= 2n, once each to form a sequence of n sets, each having 1 or 2 elements.at n=5A105749
• Triangle read by rows: T(n,k) is the number of permutations of {1,2,...,n} having genus k (see first comment for definition of genus).at n=46A177267
• Table A(d,n) of the number of paths of a chess rook in a d-dimensional hypercube from (0...0) to (n...n) where the rook may move in steps that are multiples of (1,0..0), (0,1,0..0), ..., (0..0,1).at n=23A181731
• The number of paths of a chess rook in a 5D hypercube, from (0..0) to (n..n), where the rook may move in steps that are multiples of (1,0..0), (0,1,0..0), ..., (0..0,1).at n=2A181750
• Numbers with prime factorization p*q*r*s*t*u^3 (where p, q, r, s, t, u are distinct primes).at n=11A190378
• Numbers k such that the sum of the distinct prime divisors of k equals three times the largest prime divisor of k.at n=24A200090
• Denominators of first derivatives of Catalan numbers (as continuous functions of n).at n=16A260631
• Least positive integer k such that both k and k*n belong to the set {m>0: m+1, m^2+1 and m^2+prime(m)^2 are all prime}.at n=31A261339
• Triangle read by rows: T(n,f) is the number of rooted maps with n edges and f faces on an orientable surface of genus 1.at n=28A269921
• Triangle read by rows: T(n,g) is the number of rooted maps with n edges and 8 faces on an orientable surface of genus g.at n=3A270412
• Numbers n such that the multiplicative group modulo n is the direct product of 7 cyclic groups.at n=11A272597
• Numbers k such that k+1 is a prime, k+2 is twice a prime, k+3 is three times a prime, and k+4 is four times a prime.at n=11A278585
• Triangle read by rows: T(n,k) = binomial(2*n+1, 2*k+1)*binomial(2*n-2*k, n-k)/(n+1-k) for 0 <= k <= n.at n=37A281000
• a(n) is the number of rooted maps with n edges and 8 faces on an orientable surface of genus 1.at n=0A287048
• Triangle read by rows: T(n,k) is the number of rooted toroidal maps with n edges and k faces and without isthmuses, n >= 2, k = 1..n-1.at n=35A343092
• a(n) = lcm({i + 1, i = 0..n}) / Product_{d | n, d + 1 prime} d.at n=18A362989