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

1,1

Links

Table of n, a(n) for n=1..76.

Formula

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

Example

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

Mathematica

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

Prog

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

Crossrefs

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

Cf. A007605 (sum of digits of primes).

Sequence in context: A129808 A330384 A077649 * A329423 A132025 A200363

Adjacent sequences: A308372 A308373 A308374 * A308376 A308377 A308378

Keyword

nonn,easy,base

Author

Kei Ryan, May 27 2019

Status

approved