A006375 Number of reduced indefinite binary forms of determinant -n. (Formerly M0080)

2, 1, 1, 3, 2, 1, 1, 2, 4, 2, 1, 2, 2, 1, 2, 5, 2, 2, 1, 3, 2, 1, 1, 3, 6, 2, 2, 2, 2, 2, 1, 3, 2, 2, 2, 7, 3, 1, 2, 4, 2, 2, 1, 2, 4, 1, 1, 4, 6, 3, 2, 3, 2, 2, 2, 3, 2, 2, 1, 4, 2, 1, 3, 8, 2, 2, 1, 3, 2, 2

Offset

1,1

References

J. H. Conway and N. J. A. Sloane, "Sphere Packings, Lattices and Groups", Springer-Verlag, p. 362.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

Table of n, a(n) for n=1..70.

Nachum Dershowitz, Touchard’s Drunkard, Journal of Integer Sequences, Vol. 20 (2017), #17.1.5.

Crossrefs

Cf. A006371, A006374.

Sequence in context: A066099 A254111 A234246 * A327520 A184441 A172279

Adjacent sequences: A006372 A006373 A006374 * A006376 A006377 A006378

Keyword

nonn,hard

Author

N. J. A. Sloane.

Extensions

Corrected Apr 15 1995

Status

approved