A175520 Number of distinct transpositions of digits (zeros and units) in n-th semiprime written in base 2.

3, 3, 6, 6, 4, 1, 10, 10, 10, 10, 15, 15, 20, 20, 15, 15, 20, 15, 6, 15, 15, 6, 21, 35, 35, 35, 35, 35, 35, 21, 21, 21, 21, 7, 35, 7, 21, 21, 7, 21, 21, 7, 28, 56, 56, 70, 70, 56, 56, 56, 56, 56, 28, 56, 70, 70, 70, 70, 28, 56, 28, 56, 70, 70, 56, 56, 56, 70, 56, 56, 28, 56, 56, 28

Offset: 1

Author

Juri-Stepan Gerasimov, Jun 05 2010

Keywords

• nonn
• base

Examples

			a(1)=3 because (100,010,001) where semiprime(1)=3=100 (in base 2).
		

Crossrefs

Cf. A177687.

Formula

a(n)=binomial ( (A000120(s)+A023416(s)), A000120(s) ), where s=semiprime(n).

Extensions

a(56) corrected by R. J. Mathar, Jun 07 2010