A080356 - OEIS

A080356

Number of twin primes between n and 2n: a(n) = number of j in range n <= j <= 2*n such that j and j+2 are primes.

0, 1, 2, 1, 1, 1, 1, 1, 2, 2, 2, 1, 1, 1, 2, 2, 2, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 6, 6, 6, 7, 7, 7, 6, 6, 6, 6

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OFFSET

1,3

LINKS

T. D. Noe, Table of n, a(n) for n=1..10000

EXAMPLE

n=36: between 36 and 72 the primes p such that (p,p+2) is a pair of twin primes are {41,59,71}, so a(36)=3.

MATHEMATICA

Table[Count[Table[PrimeQ[j]&&PrimeQ[j+2], {j, n, 2*n}], True], {n, 1, 1000}]

CROSSREFS

Cf. A001359, A071538.

Sequence in context: A073454 A382288 A124765 * A184167 A352085 A036541