21127

Appears in sequences

• Centered icosahedral (or cuboctahedral) numbers, also crystal ball sequence for f.c.c. lattice.at n=18A005902
• Number of solutions to c(1)*prime(4) + ... + c(n)*prime(n+3) = 0, where c(i) = +-1 for i>1, c(1) = 1.at n=23A022903
• Numbers k > 1 such that, in base 6, k and k^2 contain the same digits in the same proportion.at n=5A061660
• Expansion of 1/(x^k*(1-x-2*x^(k+1))) for k=6.at n=31A143449
• Eigensequence of triangle A084938.at n=9A165489
• Triangle read by rows, A084938 * A165489 diagonalized as an infinite lower triangular matrix.at n=54A165490
• Base-3 Keith numbers.at n=20A188195
• Number of (w,x,y,z) with all terms in {1,...,n} and |w-x| = 2*|x-y| - |y-z|.at n=37A212578
• Number of (w,x,y) with all terms in {0,...,n} and |w-x| + |x-y| + |y-w| >= w + x + y.at n=41A213489
• The 360 degree spoke (or ray) of a hexagonal spiral of Ulam.at n=42A244803
• a(n) = 2*A090495(n) - 1.at n=39A274297
• Number of finite sets of positive integers whose right half (exclusive) sums to n.at n=45A360954
• Expansion of (1/x) * Series_Reversion( x*(1+x-x^3)/(1+x)^2 ).at n=13A366095
• Numerators of the partial sums of the reciprocals of the sum of bi-unitary divisors function (A188999).at n=17A379615
• Composite numbers in A381019 which are immediately followed by another composite number, in order of their appearance.at n=25A379810
• Numbers k whose binary expansion contains 2 adjacent 1's and A391571(k) = k.at n=41A391581