A270573 Let c be the n-th composite number. a(n) is the number of composites d < c such that c^(d-1) == 1 (mod d) and d^(c-1) == 1 (mod c).

0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 2, 0, 1, 0, 0, 0, 1, 0, 2, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 3, 0, 1, 0, 0, 6, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 1, 1, 0, 1, 0, 1, 0

Offset

1,38

Links

Felix Fröhlich, Table of n, a(n) for n = 1..10000

Prog

(PARI) forcomposite(c=1, 100, my(i=0); forcomposite(d=1, c-1, if(Mod(c, d)^(d-1)==1 && Mod(d, c)^(c-1)==1, i++)); print1(i, ", "))

Crossrefs

Cf. A270574, A270575.

Sequence in context: A070097 A202523 A215935 * A096271 A285640 A231189

Adjacent sequences: A270570 A270571 A270572 * A270574 A270575 A270576

Keyword

nonn

Author

Felix Fröhlich, Mar 19 2016

Status

approved