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A164931 n times the n-th noncomposite. 4
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 (list; graph; refs; listen; history; text; internal format)
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: A177441 A241944 A256054 * A066186 A346558 A059403
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

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Last modified May 27 20:38 EDT 2024. Contains 372882 sequences. (Running on oeis4.)