%I #26 May 10 2021 07:40:02
%S 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,
%T 17,27,19,14,15,16,11,30,31,17,18,19,23,33,7,20,21,31,17,27,28,23,15,
%U 34,20,21,13,26,36,19,32,24,34,20,12,13,26,18,10,23,24,16
%N The digit sum of n*(n^2 + 1)/2.
%F a(n) = A007953(A006003(n)).
%t a[n_] := Plus @@ IntegerDigits[n*(n^2 + 1)/2]; Array[a, 100] (* _Amiram Eldar_, Aug 10 2020 *)
%o (Python)
%o def seq(num):
%o res = []
%o for i in range(1, num + 1):
%o res.append(calc(i))
%o return res
%o def calc(num):
%o sum = 0
%o start = int((num * (num - 1)) // 2) + 1
%o for i in range(start, start + num):
%o sum += i
%o recip = 0
%o for i in str(sum):
%o recip += int(i)
%o return recip
%o print(seq(260))
%o (PARI) a(n) = sumdigits(n*(n^2 + 1)/2) \\ _Michel Marcus_, Aug 10 2020
%Y Cf. A007953, A006003.
%K nonn,base
%O 1,2
%A _Páll Ivan Slamnig_, Aug 05 2020