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A175520
Number of distinct transpositions of digits (zeros and units) in n-th semiprime written in base 2.
0
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
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
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
a(56) corrected by R. J. Mathar, Jun 07 2010
STATUS
approved