A048983 As n runs through composite numbers, a(n) = number of composite d < n such that gcd(d,n) = 1.

0, 0, 0, 2, 1, 0, 1, 3, 2, 0, 1, 5, 3, 0, 11, 4, 9, 4, 0, 5, 10, 6, 14, 2, 7, 13, 5, 1, 7, 11, 9, 2, 27, 6, 18, 10, 3, 25, 9, 21, 13, 1, 13, 19, 14, 31, 4, 14, 26, 7, 5, 16, 20, 16, 40, 5, 11, 32, 19, 3, 42, 20, 34, 18, 2, 49, 21, 37, 23, 49, 9, 18

Offset

1,4

Links

Table of n, a(n) for n=1..72.

Formula

a(n) = A048984(n) - 1. Michel Marcus, Jul 14 2013

Example

9 is 4th composite number, gcd(9,4) = gcd(9,8) = 1, so a(4) = 2.

Prog

(PARI) lista(nn) = {forcomposite (n=1, nn, nb = 0; forcomposite(d=1, n-1, if (gcd(n, d) == 1, nb++)); print1(nb, ", "); ); } \\ Michel Marcus, Jul 14 2013

Crossrefs

Cf. A000010, A048984, A002808.

Sequence in context: A268387 A136566 A330235 * A301505 A301504 A307432

Adjacent sequences: A048980 A048981 A048982 * A048984 A048985 A048986

Keyword

easy,nonn

Author

Naohiro Nomoto

Status

approved