A004157 Sum of digits of n-th triangular number.

0, 1, 3, 6, 1, 6, 3, 10, 9, 9, 10, 12, 15, 10, 6, 3, 10, 9, 9, 10, 3, 6, 10, 15, 3, 10, 9, 18, 10, 12, 15, 19, 15, 12, 19, 9, 18, 10, 12, 15, 10, 15, 12, 19, 18, 9, 10, 12, 15, 10, 15, 12, 19, 9, 18, 10, 21, 15, 10, 15, 12, 19, 18, 9, 10, 12, 6, 19, 15, 12, 19, 18, 18, 10, 21, 15, 19, 6, 12, 10

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• base

Links

• Robert Israel, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A000217, A007953, A062688, A145389.

Programs

Magma

[&+Intseq(n*(n+1) div 2): n in [0..80] ]; // Vincenzo Librandi, Jun 18 2015

Maple

seq(convert(convert(n*(n+1)/2,base,10),`+`), n=0..100); # Robert Israel, Jun 18 2015

Mathematica

Table[Plus@@IntegerDigits@(n (n + 1) / 2), {n, 0, 90}] (* Vincenzo Librandi, Jun 18 2015 *)
Total[IntegerDigits[#]]&/@Accumulate[Range[0,100]] (* Harvey P. Dale, Mar 31 2024 *)

PARI

a(n) = sumdigits(n*(n+1)/2); \\ Michel Marcus, Jun 18 2015

Formula

a(n) = A007953(A000217(n)). - Robert Israel, Jun 18 2015