A004155 Sum of digits of n-th odd number.

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

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• base
• easy

Links

• G. C. Greubel, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A004092, A007953.

Programs

Mathematica

Table[Sum[DigitCount[2*n + 1][[i]]*i, {i, 9}], {n, 0, 100}] (* G. C. Greubel, Jun 19 2016 *)

PARI

a(n)=sumdigits(2*n+1) \\ Charles R Greathouse IV, Jun 19 2016

Formula

a(n) = 2n - 1 - 9*Sum_{k=1..1+floor(log_10(2n-1))} floor( (n-1)/(5*10^(k-1)) ). - Anthony Browne, Jun 18 2016

a(n) = A004092(n+5). - G. C. Greubel, Jun 19 2016