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A163489 Indices n such that composite(n)/3 is prime. 0

%I #12 Aug 06 2022 17:24:33

%S 2,4,8,12,21,26,35,40,49,63,68,81,92,97,106,121,136,140,154,165,171,

%T 185,195,210,229,240,245,254,260,270,305,315,330,336,360,365,379,395,

%U 405,421,437,442,467,472,483,488,517,547,557,562,573,589,594,619,634,650

%N Indices n such that composite(n)/3 is prime.

%e a(1)=2 (2nd composite/3 = 6/3 = 2, which is prime).

%e a(2)=4 (4th composite/3 = 9/3 = 3, which is prime).

%t Position[Select[Range[1000],CompositeQ],_?(PrimeQ[#/3]&)]//Flatten (* _Harvey P. Dale_, Aug 06 2022 *)

%Y Cf. A000040, A002808.

%K nonn,easy

%O 1,1

%A _Juri-Stepan Gerasimov_, Jul 29 2009

%E 48 replaced by 49, 62 replaced by 63, 96 by 97, etc. - _R. J. Mathar_, Oct 09 2009

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)