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.
18 is in the sequence because A125204(18) = A125204(19) = 266.
l = {0, 1}; Do[x = l[[n]] + l[[Mod[l[[n]], n] + 1]]; If[x == l[[n]], Print[n - 1]]; AppendTo[l, x], {n, 2, 10^9}]
a:= proc(n) option remember; `if`(n<2, 1,
a(n-1)+a(irem((a(n-1)-1), n)))
end:
seq(a(n), n=0..50); # Alois P. Heinz, Apr 08 2016
a[0] = a[1] = 1; a[n_] := a[n] = # + a@ Mod[# - 1, n] &@ a[n - 1]; Array[a, 47, 0] (* Michael De Vlieger, Apr 08 2016 *)
lista(nn) = {va = vector(nn); print1(va[1] = 1, ", "); print1(va[2] = 1, ", "); for (n=3, nn, va[n] = va[n-1] + va[((va[n-1]-1) % (n-1))+1]; print1(va[n], ", "););} \\ Michel Marcus, Apr 08 2016
from sympy.core.cache import cacheit @cacheit def a(n): return 1 if n<2 else a(n - 1) + a((a(n - 1) - 1)%n) print([a(n) for n in range(51)]) # Indranil Ghosh, Aug 06 2017