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A006375 Number of reduced indefinite binary forms of determinant -n.
(Formerly M0080)
1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified April 8 05:55 EDT 2020. Contains 333312 sequences. (Running on oeis4.)