A128435 a(0)=a(1)=1. For n >= 2, a(n) = number of positive integers which are <= n and are coprime to a(n-1)*a(n-2).

1, 1, 2, 2, 2, 3, 2, 3, 3, 6, 3, 4, 4, 7, 6, 4, 5, 7, 13, 16, 9, 7, 13, 19, 22, 11, 12, 8, 9, 10, 8, 13, 15, 16, 9, 12, 12, 13, 12, 12, 13, 13, 39, 27, 28, 13, 18, 15, 13, 25, 37, 40, 20, 22, 20, 20, 22, 21, 14, 17, 24, 20, 17, 24, 20, 17, 24, 22, 21, 18, 20, 19, 27, 47, 49, 64, 33, 23

Offset

0,3

Links

Table of n, a(n) for n=0..77.

Example

a(7)*a(6) = 6. So a(8) is the number of positive integers which are <= 8 and are coprime to 6. There are 3 such integers (1,5,7), so a(8) = 3.

Maple

a[0]:=1: a[1]:=1: for n from 2 to 100 do ct:=0: for i from 1 to n do if igcd(i, a[n-1]*a[n-2])=1 then ct:=ct+1 else fi: od: a[n]:=ct: od: seq(a[n], n=0..100); # Emeric Deutsch, May 06 2007

Crossrefs

Sequence in context: A050331 A259194 A194344 * A369219 A220415 A330861

Adjacent sequences: A128432 A128433 A128434 * A128436 A128437 A128438

Keyword

nonn

Author

Leroy Quet, May 05 2007

Extensions

More terms from Emeric Deutsch, May 06 2007

Status

approved