19761

Appears in sequences

• Partial sums of sequence (essentially A002378): 1, 2, 6, 12, 20, 30, 42, 56, 72, 90, ...at n=38A064999
• Interprimes (A024675) which are of the form s*prime, s=21.at n=36A075296
• Numbers m such that f(k) * 2^m - 1 is prime, where f(j) = A070826(j) and k is the number of decimal digits of 2^m.at n=36A095991
• Number of length n binary sequences with at most 4 of every adjacent 6 bits set.at n=15A133552
• This is to A139025 as A139025 to A014688, see A139025 for details.at n=33A139026
• Number of n X n binary arrays symmetric under 180 degree rotation with all ones connected only in a 110-111-111 pattern in any orientation.at n=10A146279
• Numbers k such that A(k+1) = A(k) + 1, where A() = A005101() are the abundant numbers.at n=18A169822
• Compound filter: a(n) = P(sigma(n), sigma(2n)), where P(n,k) is sequence A000027 used as a pairing function, and sigma is the sum of divisors (A000203).at n=37A286359
• Integers which can be written in exactly three ways as sum of two distinct nonzero pentagonal numbers.at n=17A333013