

A091591


Number of pairs of twin primes between n^2 and (n+1)^2.


4



1, 1, 1, 1, 1, 1, 0, 2, 1, 1, 2, 1, 2, 2, 1, 1, 0, 2, 1, 1, 1, 2, 2, 0, 0, 3, 2, 0, 1, 3, 2, 0, 3, 2, 1, 3, 0, 3, 2, 1, 3, 2, 4, 2, 2, 3, 0, 2, 2, 4, 0, 2, 1, 1, 5, 4, 4, 1, 2, 3, 4, 3, 5, 2, 2, 3, 2, 4, 1, 2, 2, 3, 4, 3, 0, 3, 3, 2, 4, 5, 2, 2, 3, 4, 1, 2, 3, 2, 3, 3, 1, 5, 1, 3, 4, 4, 2, 5, 3, 4, 1, 3, 5, 1, 2
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OFFSET

3,8


COMMENTS

a(1) and a(2) are omitted because they are dependent on the treatment of the twin pair (3,5). It is conjectured that a(n)>0 for all n>122. Proving this would also prove the twin prime conjecture.
Proving a(n)>0 for n>122 would also prove Legendre's conjecture that there is a prime between n^2 and (n+1)^2.  T. D. Noe, Feb 28 2007


LINKS

T. D. Noe, Table of n, a(n) for n=3..10000
Eric Weisstein's World of Mathematics, Twin Prime Conjecture.


EXAMPLE

a(3)=1 because the interval [3^2,4^2] contains one pair of twins (11,13).
a(9)=0 because the interval [9^2,10^2] is one of the few known intervals (given in A091592) not containing twin primes.


MATHEMATICA

a[n_] := (k = 0; For[p = NextPrime[n^2], p <= NextPrime[(n + 1)^2, 2], q = NextPrime[p]; If[q  p == 2, k++; p = NextPrime[q], p = q]]; k); Table[a[n], {n, 3, 107}] (* JeanFrançois Alcover, Jun 13 2012 *)
With[{tps=Select[Partition[Prime[Range[2000]], 2, 1], Last[#]First[#] == 2&]}, Table[ Count[tps, _?(#[[1]]>n^2&&#[[2]]<(n+1)^2&)], {n, 3, 110}]] (* Harvey P. Dale, Feb 19 2013 *)


CROSSREFS

Cf. A000290, A001359, A006512, A091592.
Cf. A014085 (number of primes between n^2 and (n+1)^2)
Sequence in context: A122901 A001917 A240545 * A337633 A227796 A109374
Adjacent sequences: A091588 A091589 A091590 * A091592 A091593 A091594


KEYWORD

easy,nonn,nice


AUTHOR

Hugo Pfoertner, Jan 22 2004


STATUS

approved



