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 A336857 The digit sum of n*(n^2 + 1)/2. 0
 1, 5, 6, 7, 11, 3, 13, 8, 18, 10, 14, 15, 7, 20, 21, 13, 17, 18, 19, 5, 15, 16, 20, 21, 22, 17, 27, 19, 14, 15, 16, 11, 30, 31, 17, 18, 19, 23, 33, 7, 20, 21, 31, 17, 27, 28, 23, 15, 34, 20, 21, 13, 26, 36, 19, 32, 24, 34, 20, 12, 13, 26, 18, 10, 23, 24, 16 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Table of n, a(n) for n=1..67. FORMULA a(n) = A007953(A006003(n)). MATHEMATICA a[n_] := Plus @@ IntegerDigits[n*(n^2 + 1)/2]; Array[a, 100] (* Amiram Eldar, Aug 10 2020 *) PROG (Python) def seq(num): res = [] for i in range(1, num + 1): res.append(calc(i)) return res def calc(num): sum = 0 start = int((num * (num - 1)) // 2) + 1 for i in range(start, start + num): sum += i recip = 0 for i in str(sum): recip += int(i) return recip print(seq(260)) (PARI) a(n) = sumdigits(n*(n^2 + 1)/2) \\ Michel Marcus, Aug 10 2020 CROSSREFS Cf. A007953, A006003. Sequence in context: A308193 A179274 A104122 * A049467 A131503 A047266 Adjacent sequences: A336854 A336855 A336856 * A336858 A336859 A336860 KEYWORD nonn,base AUTHOR Páll Ivan Slamnig, Aug 05 2020 STATUS approved

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Last modified August 8 12:42 EDT 2024. Contains 375021 sequences. (Running on oeis4.)