A108128 Number of distinct prime factors of concatenated twin primes.

2, 2, 2, 2, 2, 2, 3, 2, 3, 2, 2, 2, 2, 2, 2, 3, 2, 3, 2, 3, 3, 3, 3, 3, 3, 2, 2, 3, 2, 2, 3, 2, 2, 3, 2, 3, 3, 2, 2, 2, 3, 2, 3, 3, 3, 3, 2, 3, 2, 4, 3, 2, 2, 3, 2, 2, 2, 2, 3, 3, 2, 2, 3, 2, 2, 3, 2, 3, 3, 2, 2, 2, 3, 2, 2, 3, 2, 2, 3, 2, 3, 3, 2, 3, 4, 2, 2, 3, 3, 3, 3, 3, 2, 2, 3, 2, 2, 3, 3, 2, 2, 3, 2, 3, 2

Offset

1,1

Links

Table of n, a(n) for n=1..105.

Chris Caldwell, The First 1,008 Twin Primes.

Example

The number of distinct prime factors of 35 (which is obtained from concatenating the twin primes 3 and 5) is 2, which is the first term of the sequence.

Mathematica

Length[ FactorInteger[ # ]] & /@ FromDigits /@ Transpose[{Select[ Prime[ Range[550]], PrimeQ[ # + 2] &], Select[ Prime[ Range[550]], PrimeQ[ # - 2] &]}] (* Robert G. Wilson v, Jun 09 2005 *)

Crossrefs

Cf. A001359, A006512, A077800.

Sequence in context: A141256 A122921 A174273 * A081326 A277879 A257071

Adjacent sequences: A108125 A108126 A108127 * A108129 A108130 A108131

Keyword

nonn,base

Author

Parthasarathy Nambi, Jun 04 2005

Extensions

Edited, corrected and extended by Robert G. Wilson v, Jun 09 2005

Status

approved