A163127 a(1)=1. a(n) is the number of integers k, 1 <= k <= n-1, where gcd(a(k), n-k) >= 2.

1, 0, 0, 1, 2, 2, 3, 3, 3, 4, 4, 5, 5, 5, 5, 5, 6, 6, 7, 8, 8, 8, 8, 9, 9, 11, 11, 10, 9, 11, 10, 12, 14, 12, 13, 14, 14, 16, 14, 17, 16, 15, 18, 17, 18, 18, 20, 20, 21, 18, 20, 23, 23, 22, 22, 23, 24, 22, 24, 25, 28, 24, 29, 23, 28, 27, 28, 26, 29, 26, 30, 30, 31, 32, 33, 31, 32, 31

Offset

1,5

Comments

For the purpose of this sequence, gcd(m,0) is considered to be m.

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

f:= proc(n) option remember;
       nops(select(k -> igcd(f(k), n-k)>=2, [$1..n-1]))
end proc:
f(1):= 1:
map(f, [$1..100]); # Robert Israel, Jun 16 2025

Crossrefs

Cf. A163126.

Sequence in context: A330393 A273263 A274533 * A077113 A143796 A245473

Adjacent sequences: A163124 A163125 A163126 * A163128 A163129 A163130

Keyword

nonn

Author

Leroy Quet, Jul 21 2009

Extensions

More terms from Sean A. Irvine, Oct 20 2009

Status

approved