A089994 Number of primes between factors of n-th semiprime.

0, 0, 0, 1, 2, 0, 1, 3, 0, 4, 2, 5, 0, 6, 3, 7, 0, 4, 1, 5, 8, 9, 2, 6, 10, 0, 11, 3, 12, 7, 1, 8, 13, 4, 14, 9, 5, 15, 2, 0, 16, 10, 11, 3, 17, 12, 18, 0, 6, 19, 7, 20, 13, 4, 21, 0, 14, 22, 15, 8, 1, 23, 16, 24, 5, 9, 25, 2, 17, 26, 10, 6, 27, 18, 0, 28, 11, 19, 1, 20, 3, 29, 7, 30

Offset: 1

Author

Reinhard Zumkeller, Nov 19 2003

Keywords

• nonn

Comments

a(m)=0 iff m in A033476; a(m)>0 iff m in A089995.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001358, A033476, A089995, A084126, A084127, A000720.

Programs

Mathematica

pbfs[n_]:=Module[{f=PrimePi/@Transpose[FactorInteger[n]][[1]]}, Max[ 0,Last[f]-First[f]-1]]; pbfs/@Select[Range[300],PrimeOmega[#]==2&] (* Harvey P. Dale, Apr 09 2012 *)