A127433 a(1)=1. a(n) = number of earlier terms a(k), 1<=k<=n-1, such that (k+n) is coprime to a(k).

1, 1, 2, 3, 2, 5, 4, 6, 4, 8, 5, 9, 7, 8, 8, 12, 9, 12, 9, 12, 13, 13, 14, 14, 14, 15, 17, 18, 13, 19, 18, 20, 21, 20, 22, 21, 22, 23, 20, 25, 22, 27, 23, 25, 26, 29, 29, 33, 27, 33, 29, 37, 32, 33, 33, 36, 33, 40, 34, 37, 37, 40, 37, 42, 38, 40, 41, 45, 37, 47, 42, 46, 45, 48, 46

Offset

1,3

Links

Table of n, a(n) for n=1..75.

Example

(1+9) is coprime to a(1)=1; (2+9) is coprime to a(2)=1; (4+9) is coprime to a(4)=3 and (8+9) is coprime to a(8)=6. These four cases are the only cases where (k+n) is coprime to a(k), for 1<=k<=8. So a(9) = 4.

Mathematica

f[l_List] := Block[{n = Length[l] + 1}, Append[l, Count[Table[GCD[k + n, l[[k]]], {k, n - 1}], 1]]]; Nest[f, {1}, 75] (* Ray Chandler, Jan 22 2007 *)

Crossrefs

Cf. A127431, A127434.

Sequence in context: A232113 A216475 A267807 * A055573 A238729 A182816

Adjacent sequences: A127430 A127431 A127432 * A127434 A127435 A127436

Keyword

nonn

Author

Leroy Quet, Jan 14 2007

Extensions

Extended by Ray Chandler, Jan 22 2007

Status

approved