A308339 Sphenic number indices of A215217.

21, 30, 49, 51, 75, 82, 96, 106, 120, 130, 133, 136, 141, 148, 152, 157, 161, 173, 177, 180, 186, 187, 189, 202, 207, 209, 213, 217, 221, 226, 236, 240, 242, 244, 248, 261, 264, 277, 285, 286, 294, 305, 306, 311, 317, 320, 322, 327, 333, 349, 355, 364, 368

Offset: 1

Author

Peter Dolland, May 20 2019

Keywords

• nonn

Comments

A215217 is a subsequence of A007304 (by definition). The index sequence is more compact.

Examples

			For n = 3: a(3) = 49 and A215217(3) = 429 = A007304(49).
		

Links

• Peter Dolland, Table of n, a(n) for n = 1..200

Crossrefs

Cf. A007304, A215217.

Programs

Haskell

twinLowX [] = []
twinLowX [_] = []
twinLowX (n : (m : ns))
    | m == n + 1 = 1 : (map succ (twinLowX (m : ns)))
    | otherwise = (map succ (twinLowX (m : ns)))
a308339 n = (twinLowX a007304_list) !! (n - 1)
-- Peter Dolland, May 31 2019

Formula

A215217(n) = A007304(a(n)).