Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 5000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
Table of n, a(n) for n=0..79.
a(n)= binomial ((A000120(n-1)+A023416(n-1)), A000120(n-1)).
a(0)=1 because 0 (or 0 written in base 2), a(1)=1 because 1 (or 1 written in base 2), a(3)= 2 (or 10 written in base 2) and (01,10)=distinct transpositions.
Sequence in context: A264154 A099246 A039775 * A227532 A152534 A136018
Adjacent sequences: A178241 A178242 A178243 * A178245 A178246 A178247
Juri-Stepan Gerasimov, May 23 2010
Corrected (a 3 in the first group removed) by R. J. Mathar, May 28 2010