A007104 Number of elements (a b, c d) in GL(2,Z) with det = -1, trace n and 0 <= a <= {b, c} <= d.

1, 1, 1, 2, 1, 4, 1, 4, 4, 4, 2, 10, 1, 5, 7, 12, 1, 10, 4, 10, 12, 4, 6, 24, 4, 12, 7, 10, 5, 26, 6, 20, 13, 12, 7, 30, 11, 4, 15, 32, 6, 26, 6, 28, 23, 12, 7, 52, 12, 10, 28, 10, 6, 40, 14, 44, 17, 24, 12, 56, 19, 12, 20, 36, 27, 44, 11, 28, 16

Offset

1,4

Links

Sean A. Irvine, Table of n, a(n) for n = 1..250

Prog

(PARI)
D(n, s, t)={if(n>=1, sumdiv(n, d, s<=min(d, n/d) && max(d, n/d)<=t), 0)}
a(n)={sum(i=0, n\2, D(i*(n-i)+1, i, n-i))} \\ Andrew Howroyd, Jan 01 2020

Crossrefs

Cf. A006546, A007203.

Sequence in context: A051953 A079277 A066452 * A102627 A296560 A284652

Adjacent sequences: A007101 A007102 A007103 * A007105 A007106 A007107

Keyword

nonn

Author

John Lewis (frc.mass.edu)

Extensions

More terms from Sean A. Irvine, Oct 12 2017

Status

approved