A004092 Sum of digits of even numbers.

0, 2, 4, 6, 8, 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, 1, 3, 5

Offset: 0

Author

N. J. A. Sloane, Dec 11 1996

Keywords

• nonn
• base
• easy

Comments

a(n) >= A007953(n) / 5 with equality iff n is in A169964 (see Diophante link). - Bernard Schott, Apr 29 2023

Links

• G. C. Greubel, Table of n, a(n) for n = 0..10000
• Diophante, A1762, Des chiffres à la moulinette (in French).

Crossrefs

Cf. A007953, A169964.

Programs

Mathematica

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

PARI

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

Formula

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

a(n) = A007953(2n). - Alois P. Heinz, Apr 11 2018