A178043 n-th semiprime minus number of distinct transpositions of digits (zeros and units) in n-th semiprime written in base 2.

1, 3, 3, 4, 10, 14, 11, 12, 15, 16, 18, 19, 15, 18, 24, 31, 29, 36, 49, 42, 43, 56, 44, 34, 39, 42, 47, 50, 51, 66, 70, 72, 73, 88, 71, 104, 94, 97, 112, 100, 101, 116, 101, 77, 78, 71, 72, 87, 89, 90, 99, 102, 131, 105, 96, 99, 107, 108, 155, 129, 159, 138, 131, 132, 147

Offset

1,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Formula

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

Mathematica

#-Length[Permutations[IntegerDigits[#, 2]]]&/@Select[Range[ 2, 300], PrimeOmega[ #] == 2&] (* Harvey P. Dale, Jun 21 2014 *)

Crossrefs

Cf. A001358, A122466.

Sequence in context: A368224 A144626 A033707 * A049925 A362107 A364910

Adjacent sequences: A178040 A178041 A178042 * A178044 A178045 A178046

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, May 17 2010

Extensions

More terms from R. J. Mathar, May 28 2010

Status

approved