A308375 Digital sum of composite numbers.

4, 6, 8, 9, 1, 3, 5, 6, 7, 9, 2, 3, 4, 6, 7, 8, 9, 10, 3, 5, 6, 7, 8, 9, 11, 12, 4, 6, 8, 9, 10, 12, 13, 5, 6, 7, 9, 10, 11, 12, 13, 6, 8, 9, 10, 11, 12, 14, 15, 7, 9, 11, 12, 13, 14, 15, 8, 9, 10, 12, 13, 14, 15, 16, 9, 10, 11, 12, 13, 14, 15, 17, 18, 1, 3, 5

Offset: 1

Author

Kei Ryan, May 27 2019

Keywords

• nonn
• easy
• base

Examples

			The 6th term is 3 because the digital sum of 12 (the 6th composite number) is 3 (1+2).
		

Crossrefs

Cf. A002808 (composite numbers), A007953 (sum of digits).

Cf. A007605 (sum of digits of primes).

Programs

Mathematica

Total /@ IntegerDigits /@ Select[Range[104], CompositeQ] (* Giovanni Resta, May 28 2019 *)

PARI

lista(nn) = forcomposite(n=1, nn, print1(sumdigits(n), ", ")); \\ Michel Marcus, May 28 2019

Formula

a(n) = A007953(A002808(n)).