A127431 a(1)=1. a(n) = number of earlier terms a(k), 1<=k<=n-1, such that (k+n) is divisible by a(k).

1, 1, 2, 2, 3, 3, 4, 3, 5, 5, 4, 4, 7, 3, 6, 8, 5, 5, 6, 5, 8, 8, 5, 6, 10, 5, 8, 8, 9, 7, 7, 8, 9, 9, 8, 9, 12, 5, 8, 12, 8, 9, 10, 7, 13, 9, 13, 11, 10, 7, 9, 12, 11, 9, 11, 10, 18, 8, 8, 10, 16, 10, 9, 12, 11, 11, 14, 13, 13, 12, 10, 15, 12, 10, 15, 11, 15, 12, 11, 13, 14, 12, 12, 13, 18, 9, 14

Offset

1,3

Links

Rémy Sigrist, Table of n, a(n) for n = 1..10000

Rémy Sigrist, C program for A127431

Example

(1+11) is a multiple of a(1)=1; (2+11) is a multiple of a(2)=1; (3+11) is a multiple of a(3)=2; and (9+11) is a multiple of a(9)=5. These four cases are the only cases where (k+n) is divisible by a(k), for 1<=k<=10. So a(11) = 4.

Mathematica

f[l_List] := Block[{n = Length[l] + 1}, Append[l, Count[Table[Mod[k + n, l[[k]]], {k, n - 1}], 0]]]; Nest[f, {1}, 86] (* Ray Chandler, Jan 22 2007 *)

Prog

(C) See Links section.

Crossrefs

Cf. A127432, A127433.

Sequence in context: A283367 A322528 A258756 * A289777 A182921 A291268

Adjacent sequences: A127428 A127429 A127430 * A127432 A127433 A127434

Keyword

nonn,look

Author

Leroy Quet, Jan 14 2007

Extensions

Extended by Ray Chandler, Jan 22 2007

Status

approved