21515
domain: N
Appears in sequences
- Fibonacci sequence beginning 4, 11.at n=17A022131
- Every prefix prime in base 6 (written in base 6).at n=23A024766
- Triangle read by rows: T(n,k) (k>=0) is the number of RNA secondary structures of size n (i.e., with n nodes) having k arcs that are covered by other arcs.at n=54A110317
- Number of obtuse triangles, distinct up to congruence, on an n X n grid (or geoboard).at n=20A190022
- Number of (n+2) X 9 0..1 matrices with each 3 X 3 subblock idempotent.at n=14A224558
- Number of ballot sequences of length n having 2 largest parts.at n=12A244099
- Intersection of A003052 and A283002.at n=33A283003
- Numbers k such that k!6 - 32 is prime, where k!6 is the sextuple factorial number (A085158).at n=28A289699