This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
# Using function A from A363733. seq(add(A(n - k, k), k = 0..n), n = 0..26);
A363913:= func< n | n eq 0 select 1 else 3*(&+[3^(d-1): d in Divisors(n)]) >; [A363913(n): n in [0..40]]; // G. C. Greubel, Jun 26 2024
divides := (k, n) -> ifelse(k = n or (k > 0 and irem(n, k) = 0), 1, 0): a := n -> local j; add(divides(j, n) * 3^j, j = 0 ..n): seq(a(n), n = 0..28);
A363913[n_]:= If[n==0, 1, 3*DivisorSum[n, 3^(#-1) &]]; Table[A363913[n], {n,0,40}] (* G. C. Greubel, Jun 26 2024 *)
from sympy import divisors def A363913(n): return sum(3**k for k in divisors(n,generator=True)) if n else 1 # Chai Wah Wu, Jun 28 2023
def a(n): return sum(3^k * k.divides(n) for k in srange(n+1)) print([a(n) for n in range(29)])