A282601 a(n) = Sum_(k=1..phi(n)/2) floor(d_k/2) where d_k are the totatives of n.

0, 0, 0, 0, 1, 0, 2, 1, 3, 1, 6, 2, 9, 3, 6, 6, 16, 5, 20, 8, 14, 10, 30, 10, 29, 15, 28, 18, 49, 14, 56, 28, 38, 28, 48, 24, 81, 36, 54, 36, 100, 30, 110, 50, 64, 55, 132, 44, 124, 57, 96, 72, 169, 56, 130, 78, 122, 91, 210, 56, 225, 105, 136, 120, 186, 80, 272, 128, 182, 102

Offset: 1

Author

Michel Marcus, Feb 19 2017

Keywords

• nonn

Comments

The totatives of n are the numbers k <= n with gcd(k,n) = 1.

Links

• David Zmiaikou, Origamis and permutation groups, Thesis, 2011. See p. 65.

Crossrefs

Cf. A000010, A023896, A038566, A066840, A282600.

Programs

PARI

a(n) = {vn = vector(n, k, k); vt = select(x->(gcd(x,n) == 1), vn); sum(k=1, #vt\2, vt[k]\2);}