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A128203 Sum of the digits of n*(n+1). 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

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

FORMULA

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

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 *)

CROSSREFS

Sequence in context: A136758 A056113 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

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Last modified February 21 10:49 EST 2019. Contains 320372 sequences. (Running on oeis4.)