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A128203
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Sum of the digits of n*(n+1).
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0
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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; internal format)
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OFFSET
| 0,2
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FORMULA
| a(n)=Sum_digits[n*(n+1)], with n>=0
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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);
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MATHEMATICA
| Table[Total[IntegerDigits[n(n+1)]], {n, 0, 80}] (* From Harvey P. Dale, May 14 2011 *)
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CROSSREFS
| Sequence in context: A011042 A136758 A056113 * A144531 A086357 A138054
Adjacent sequences: A128200 A128201 A128202 * A128204 A128205 A128206
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KEYWORD
| easy,nonn,base
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AUTHOR
| Paolo P. Lava & Giorgio Balzarotti (paoloplava(AT)gmail.com), May 03 2007
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