3121152

Appears in sequences

• Sum of digits of zero-absent composite a(n) equals number of prime factors.at n=9A050690
• Triangle read by rows, whose row sums using Euler numbers are the unsigned even-indexed Bernoulli numbers (denominators).at n=21A229097
• Triangle read by rows, whose row sums using Euler numbers are the unsigned even-indexed Bernoulli numbers (denominators).at n=27A229097
• Triangle T(n,k), n>=3, 3<=k<=n, read by rows. Number of ways to make n selections without replacement from a circular array of n unlabeled cells (ignoring rotations and reflection), such that the first selection of a cell adjacent to previously selected cells occurs on the k-th selection.at n=51A249796