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

1,1

Comments

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

Links

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

Formula

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

Example

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

Prog

(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

Crossrefs

Cf. A007304, A215217.

Sequence in context: A379019 A336357 A317772 * A186455 A318081 A276655

Adjacent sequences: A308336 A308337 A308338 * A308340 A308341 A308342

Keyword

nonn

Author

Peter Dolland, May 20 2019

Status

approved