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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. 4
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
LINKS
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
Sequence in context: A138559 A073454 A124765 * A184167 A352085 A036541
KEYWORD
nonn
AUTHOR
Labos Elemer, Feb 19 2003
EXTENSIONS
Definition clarified by N. J. A. Sloane, Aug 22 2021
STATUS
approved

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Last modified March 29 06:15 EDT 2024. Contains 371265 sequences. (Running on oeis4.)