21920

Appears in sequences

• Row 3 of array in A047666.at n=31A047667
• Number of nonprimes <= prime(n)^2.at n=36A053683
• Eighth column of triangle A055249.at n=7A055251
• Smallest k > 0 with gcd(k, rev(k)) = n, where rev(k) is digit reversal of k, or 0 if no such k exists.at n=31A069554
• Smallest solution to gcd(x, Rev(x)) = 2^n.at n=4A071686
• Numbers that have exactly seven prime factors counted with multiplicity (A046308) whose digit reversal is different and also has 7 prime factors (with multiplicity).at n=4A109027
• Row sums of correlation triangle for (1+x)^3/(1-x).at n=38A115293
• Number of 1..28 integer arrays v[1..n] of length n with all autocorrelation values sum(i){v[i]*v[i-k]} distinct for k in 0..n-1.at n=2A171302
• Number of 1..n integer arrays v[1..3] of length 3 with all autocorrelation values sum(i){v[i]*v[i-k]} distinct for k in 0..2.at n=27A171340
• Number of 7 X n binary arrays without the pattern 0 1 diagonally, vertically, antidiagonally or horizontally.at n=14A188558
• Number of (n+5)X(n+5) 0..1 matrices with each 6X6 subblock idempotent.at n=8A224569
• Triangle read by rows: Number of (2n+1)-step self-avoiding walks on diamond lattice ending at point with x = 2k+1.at n=17A227716
• Numbers m such that the GCD of the x's that satisfy sigma(x) = m is 3.at n=37A241648
• Expansion of f(x^2)^2 / f(-x) in powers of x where f() is a Ramanujan theta function.at n=37A260163
• p-INVERT of the positive integers, where p(S) = 1 - 4*S + S^2.at n=5A291026
• Numbers k such that (k - 1)^(k + 1) - k is prime.at n=10A382370
• Expansion of (1+3*x+2*x^2) / (1-6*x^2-4*x^3+2*x^4).at n=10A384635