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A108128 Number of distinct prime factors of concatenated twin primes. 0
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 24 15:33 EDT 2021. Contains 347643 sequences. (Running on oeis4.)