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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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS 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: A038167 A307967 A131077 * A271668 A072464 A262871 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

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Last modified September 27 15:29 EDT 2020. Contains 337383 sequences. (Running on oeis4.)