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

9, 11, 12, 13, 14, 15, 16, 18, 19, 21, 22, 25, 26, 28, 48, 51, 57, 60, 70, 72, 74, 78, 80, 81, 82, 86, 89, 92, 103, 109, 111, 114, 120, 125, 128, 130, 131, 142, 145, 146, 151, 155, 157, 159, 164, 168, 169, 179, 183, 185, 186, 191, 195, 197, 200, 205, 210, 211

Offset: 1

Author

Michel Lagneau, Dec 23 2011

Keywords

• nonn
• base
• changed

Comments

Numbers k such that A120390(k) is prime.

If k = 9 or k > 10, then (sum of digits of k!!) / 9 is an integer (see A120390).

Examples

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

Crossrefs

Cf. A006882, A120390.

Programs

Mathematica

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