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 A004157 Sum of digits of n-th triangular number. 3
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Robert Israel, Table of n, a(n) for n = 0..10000 FORMULA a(n) = A007953(A000217(n)). - Robert Israel, Jun 18 2015 MAPLE P:=proc(n) local a, i, k, w; a:=0; for i from 1 by 1 to n do a:=a+i; w:=0; k:=a; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; print(w); od; end: P(100); # Paolo P. Lava, May 03 2007 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 *) PROG (MAGMA) [&+Intseq(n*(n+1) div 2): n in [0..80] ]; // Vincenzo Librandi, Jun 18 2015 (PARI) a(n) = sumdigits(n*(n+1)/2); \\ Michel Marcus, Jun 18 2015 CROSSREFS Cf. A000217, A007953, A145389. Sequence in context: A134804 A145389 A055263 * A091068 A065233 A243658 Adjacent sequences:  A004154 A004155 A004156 * A004158 A004159 A004160 KEYWORD nonn,base AUTHOR STATUS approved

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Last modified June 15 20:50 EDT 2019. Contains 324145 sequences. (Running on oeis4.)