21156

Appears in sequences

• Expansion of 1/Product_{m>=1} (1 - m*q^m)^12.at n=5A022736
• Numbers k that divide the (right) concatenation of all numbers <= k written in base 3 (most significant digit on left).at n=24A029448
• Number of pentagonal regions in regular n-gon with all diagonals drawn.at n=38A067152
• Symmetric square table of coefficients, read by antidiagonals, where T(n,k) is the coefficient of x^n*y^k in f(x,y) that satisfies f(x,y) = (1-xy)/[(1-x)(1-y)] + xy*f(x,y)^3.at n=70A086626
• Symmetric square table of coefficients, read by antidiagonals, where T(n,k) is the coefficient of x^n*y^k in f(x,y) that satisfies f(x,y) = (1-xy)/[(1-x)(1-y)] + xy*f(x,y)^3.at n=73A086626
• Number of arrangements of 4 nonzero numbers x(i) in -n..n with the sum of x(i)*x(i+1) equal to zero.at n=29A188250
• Numbers k such that 2*R_k + 3*10^k + 1 is prime, where R_k = 11...11 is the repunit (A002275) of length k.at n=5A259129
• Numbers k such that (34*10^k - 403)/9 is prime.at n=18A293594
• Rank of the inverse semigroup D_n of all difunctional relations on an n-element set.at n=9A294431
• Triangle read by rows: T(n,k) (0 <= k <= n) is the rank of the ideal I_r in the inverse semigroup D_n of all difunctional relations on an n-element set.at n=54A294432
• Fixed points of A300956.at n=4A300958
• Numbers k such that prime(k+1)^prime(k+3) == prime(k) mod prime(k+2).at n=11A335571