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 A202707 Numbers n such that (sum of digits of n!!) / 9 is prime. 0

%I

%S 9,11,12,13,14,15,16,18,19,21,22,25,26,28,48,51,57,60,70,72,74,78,80,

%T 81,82,86,89,92,103,109,111,114,120,125,128,130,131,142,145,146,151,

%U 155,157,159,164,168,169,179,183,185,186,191,195,197,200,205,210,211

%N Numbers n such that (sum of digits of n!!) / 9 is prime.

%C If n = 9 and n >10, then (sum of digits of n!!) / 9 is an integer (see A120390).

%F n such that A120390(n) prime.

%e For n = 9, 9!! = 945, and (9+4+5)/9 = 2 is prime.

%t lst={}; Do[If[PrimeQ[Sum[DigitCount[n!!][[i]]*i/9,{i,1,9}]], AppendTo[lst, n]], {n,1,300}]; lst

%Y Cf. A006882, A120390.

%K nonn,base

%O 1,1

%A _Michel Lagneau_, Dec 23 2011

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Last modified May 21 00:36 EDT 2022. Contains 353886 sequences. (Running on oeis4.)