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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

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: A102245 A038167 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 March 22 04:32 EDT 2019. Contains 321406 sequences. (Running on oeis4.)