A336857 The digit sum of n*(n^2 + 1)/2.

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

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: A179274 A104122 A384445 * A049467 A131503 A047266

Adjacent sequences: A336854 A336855 A336856 * A336858 A336859 A336860

Keyword

nonn,base

Author

Páll Ivan Slamnig, Aug 05 2020

Status

approved