1,1

Table of n, a(n) for n=1..55.

A027480(k) = k * (k + 1) * (k + 2) / 2 is in the sequence for k >= 2.

There are 30 permutations of 5 balls where 2 are red, 2 are yellow and 1 is blue.

A002378 is a subsequence.

Cf. A027480, A304938.

Sequence in context: A105455 A246198 A083207 * A145278 A094371 A286927

Adjacent sequences: A304388 A304389 A304390 * A304392 A304393 A304394

nonn,easy

David A. Corneth, May 24 2018

approved