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A122170 Number of primes p <= 2n such that p+n is also a prime. 1
1, 1, 1, 2, 1, 3, 0, 3, 1, 4, 1, 5, 0, 4, 1, 4, 1, 6, 0, 4, 1, 4, 0, 10, 0, 6, 1, 5, 1, 12, 0, 5, 0, 6, 1, 13, 0, 7, 1, 9, 1, 13, 0, 7, 1, 6, 0, 13, 0, 9, 1, 7, 0, 14, 0, 12, 1, 7, 1, 19, 0, 7, 0, 10, 1, 20, 0, 11, 1, 13, 1, 15, 0, 8, 0, 10, 1, 18, 0, 12, 1, 8, 0, 23, 0, 10, 1, 10, 0, 26, 0, 13, 0, 13 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

a(n)=0 for n in A007921.

LINKS

Table of n, a(n) for n=1..94.

EXAMPLE

a(12)=5 because only the 5 primes p=5,7,11,17,19 below 24 form other primes p+12 = 17,19,23,29,31.

MATHEMATICA

Table[Length[Select[Select[Range[2*n], PrimeQ], PrimeQ[ #+n]&]], {n, 100}] (* Ryan Propper, Nov 12 2006 *)

CROSSREFS

Sequence in context: A146094 A098035 A079055 * A066029 A141198 A239621

Adjacent sequences:  A122167 A122168 A122169 * A122171 A122172 A122173

KEYWORD

nonn

AUTHOR

Lekraj Beedassy, Aug 23 2006

EXTENSIONS

More terms from Ryan Propper, Nov 12 2006

STATUS

approved

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Last modified July 16 11:09 EDT 2020. Contains 335784 sequences. (Running on oeis4.)