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.

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

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.

Sequence in context: A090904 A125295 A050649 this_sequence A000887 A118542 A007155

Adjacent sequences: A003039 A003040 A003041 this_sequence A003043 A003044 A003045

nonn,nice

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