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

1,1

Links

Table of n, a(n) for n=1..74.

Formula

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

Example

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

Crossrefs

Cf. A177687.

Sequence in context: A131077 A357897 A342511 * A271668 A370291 A072464

Adjacent sequences: A175517 A175518 A175519 * A175521 A175522 A175523

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, Jun 05 2010

Extensions

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

Status

approved