This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A202707 #13 Aug 31 2025 01:34:34
%S A202707 9,11,12,13,14,15,16,18,19,21,22,25,26,28,48,51,57,60,70,72,74,78,80,
%T A202707 81,82,86,89,92,103,109,111,114,120,125,128,130,131,142,145,146,151,
%U A202707 155,157,159,164,168,169,179,183,185,186,191,195,197,200,205,210,211
%N A202707 Numbers k such that (sum of digits of k!!) / 9 is prime.
%C A202707 Numbers k such that A120390(k) is prime.
%C A202707 If k = 9 or k > 10, then (sum of digits of k!!) / 9 is an integer (see A120390).
%e A202707 For k = 9, 9!! = 945, and (9+4+5)/9 = 2 is prime.
%t A202707 lst={}; Do[If[PrimeQ[Sum[DigitCount[n!!][[i]]*i/9,{i,1,9}]], AppendTo[lst, n]], {n,1,300}]; lst
%Y A202707 Cf. A006882, A120390.
%K A202707 nonn,base,changed
%O A202707 1,1
%A A202707 _Michel Lagneau_, Dec 23 2011