A128203 Sum of the digits of n*(n+1).

0, 2, 6, 3, 2, 3, 6, 11, 9, 9, 2, 6, 12, 11, 3, 6, 11, 9, 9, 11, 6, 12, 11, 12, 6, 11, 9, 18, 11, 15, 12, 20, 12, 6, 11, 9, 9, 11, 15, 12, 11, 12, 15, 20, 18, 9, 11, 15, 12, 11, 12, 15, 20, 18, 18, 11, 15, 12, 11, 12, 15, 20, 18, 9, 11, 15, 12, 20, 21, 15, 20, 9, 18, 11, 15, 12, 20, 12

Offset

0,2

Links

Table of n, a(n) for n=0..77.

Formula

a(n) = Sum_digits(n*(n+1)), with n>=0.

a(n) = A007953(A002378(n)). - Michel Marcus, May 08 2025

Maple

P:=proc(n) local i, k, w; for i from 0 by 1 to n do w:=0; k:=i*(i+1); while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; print(w); od; end: P(100);

Mathematica

Table[Total[IntegerDigits[n(n+1)]], {n, 0, 80}] (* Harvey P. Dale, May 14 2011 *)

Prog

(PARI) a(n) = sumdigits(n*(n+1)); \\ Amiram Eldar, May 08 2025

Crossrefs

Cf. A002378, A007953.

Sequence in context: A056113 A380714 A251755 * A144531 A086357 A138054

Adjacent sequences: A128200 A128201 A128202 * A128204 A128205 A128206

Keyword

easy,nonn,base

Author

Paolo P. Lava and Giorgio Balzarotti, May 03 2007

Status

approved