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

1,3

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.

Links

Table of n, a(n) for n=1..67.

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 *)

Prog

(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

Crossrefs

Cf. A065075.

Sequence in context: A106410 A065737 A014719 * A329732 A298816 A095873

Adjacent sequences: A139414 A139415 A139416 * A139418 A139419 A139420

Keyword

base,easy,nonn

Author

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

Extensions

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

Status

approved