A164931 n times the n-th noncomposite.

1, 4, 9, 20, 35, 66, 91, 136, 171, 230, 319, 372, 481, 574, 645, 752, 901, 1062, 1159, 1340, 1491, 1606, 1817, 1992, 2225, 2522, 2727, 2884, 3103, 3270, 3503, 4064, 4323, 4658, 4865, 5364, 5587, 5966, 6357, 6680, 7093, 7518, 7783, 8404, 8685, 9062, 9353

Offset

1,2

Comments

Does some n > 2 exist such that n * prime(n-1) / (n + prime(n-1)), i.e. a(n) / A090178(n) is an integer?

Complement of A171519. - Jaroslav Krizek, Dec 13 2009

Partial sums of A092929. - Gionata Neri, May 26 2015

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Formula

a(n) = n*A008578(n).

Mathematica

Module[{nn=200, cmps}, cmps=Select[Range[nn], !CompositeQ[#]&]; Times@@@ Thread[ {cmps, Range[Length[cmps]]}]] (* Harvey P. Dale, Jul 25 2021 *)

Prog

(PARI) a(n)=if(n>1, n*prime(n-1), 1) \\ Charles R Greathouse IV, Jun 02 2015

Crossrefs

Sequence in context: A394499 A241944 A256054 * A066186 A346558 A059403

Adjacent sequences: A164928 A164929 A164930 * A164932 A164933 A164934

Keyword

nonn,easy

Author

Jaroslav Krizek, Aug 31 2009

Extensions

Correction for change of offset in A008578 by Jaroslav Krizek, Jan 27 2010

Status

approved