A139417 Sum of digits of the square of the sum of the preceding numbers.

1, 1, 4, 9, 9, 18, 18, 9, 18, 27, 27, 27, 18, 27, 27, 18, 27, 18, 27, 18, 9, 27, 27, 27, 27, 18, 27, 9, 27, 27, 27, 9, 27, 27, 36, 27, 27, 27, 18, 27, 27, 27, 27, 27, 36, 36, 9, 27, 27, 18, 36, 36, 27, 18, 27, 18, 27, 27, 27, 27, 36, 36, 27, 18, 36, 27, 36

Offset: 1

Author

Philippe Lallouet (philip.lallouet(AT)orange.fr), Apr 20 2008

Keywords

• base
• easy
• nonn

Comments

As soon as a term is 9 or multiple of 9, which is true for a(4), all following ones are also multiple of 9, which never occurs in A065075.

Crossrefs

Cf. A065075.

Programs

Mathematica

nxt[{t_,a_}]:=Module[{c=Total[IntegerDigits[t^2]]},{t+c,c}]; NestList[ nxt,{1,1},70][[All,2]] (* Harvey P. Dale, Jun 15 2021 *)

Python

def sd(n): return sum(map(int, str(n)))
def aupton(terms):
    alst, s = [1], 1
    for n in range(2, terms+1): alst.append(sd(s**2)); s += alst[-1]
    return alst
print(aupton(67)) # Michael S. Branicky, Jun 15 2021

Extensions

Corrected and extended by Harvey P. Dale, Jun 15 2021