1,2

Finding a(6) is problem 43 in the Knuth reference. a(6) was estimated to be about 7*10^22 by Silverman, et al.

M. Gardner, Knotted Doughnuts and Other Mathematical Entertainments. Freeman, NY, 1986, p. 24.

D. E. Knuth, The Art of Computer Programming, vol. 4A, Combinatorial Algorithms, (to appear), section 7.2.1.1.

Silverman, Jerry; Vickers, Virgil E.; and Sampson, John L., Statistical estimates of the n-bit Gray codes by restricted random generation of permutations of 1 to 2^n, IEEE Trans. Inform. Theory 29 (1983), no. 6, 894-901.

Eric Weisstein's World of Mathematics, Hamiltonian Circuit

a(n) = 2 * A066037(n).

Equals A006069 divided by 2^n. Cf. A006070, A091299, A003043.

Cf. A091302.

Adjacent sequences: A003039 A003040 A003041 this_sequence A003043 A003044 A003045

Sequence in context: A090904 A125295 A050649 this_sequence A000887 A118542 A007155

nonn,nice

N. J. A. Sloane (njas(AT)research.att.com).