A046995 Greek-key tours on a 4 X n board; i.e., self-avoiding walks on 4 X n grid starting in top left corner.

1, 4, 17, 52, 160, 469, 1337, 3750, 10347, 28249, 76382, 204996, 546651, 1449952, 3828232, 10067585, 26384939, 68941126, 179658343, 467084601, 1211812016, 3138075544, 8112667259, 20941558268, 53983767498

Offset

1,2

References

Posting by Thomas Womack (mert0236(AT)sable.ox.ac.uk) to sci.math newsgroup, Apr 21 1999.

Links

Table of n, a(n) for n=1..25.

Formula

Conjecture: a(n)=3a(n-1)+3a(n-2)-9a(n-3)-6a(n-4)+5a(n-5)+a(n-6)-3a(n-7)+a(n-8) for n>=10. - Dean Hickerson, Apr 05 2003

Conjecture: G.f.: x*(-(x-1)*(x^7-x^6-2*x^5+3*x^4-2*x^3-4*x^2-2*x-1))/((x^4-2*x^3+2*x^2+2*x-1)*(x^4-x^3-3*x^2-x+1)) [From Maksym Voznyy (voznyy(AT)mail.ru), Jul 27 2009]

Crossrefs

Cf. A046994.

Sequence in context: A047668 A208658 A092091 * A001585 A060262 A157492

Adjacent sequences: A046992 A046993 A046994 * A046996 A046997 A046998

Keyword

nonn,walk

Author

Antreas P. Hatzipolakis (xpolakis(AT)otenet.gr)

Extensions

More terms from Hugo van der Sanden, Apr 02 2003

Status

approved