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A162308 Number of twin primes A001097 smaller than the non-twin prime A007510(n). 1
0, 7, 9, 11, 11, 13, 15, 15, 15, 15, 19, 19, 19, 23, 23, 23, 23, 29, 29, 31, 33, 33, 33, 35, 37, 37, 39, 39, 39, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 45, 45, 45, 45, 47, 47, 47, 47, 47, 47, 47, 49, 49, 49, 49, 51, 51, 51, 53, 53, 55, 57, 57, 59, 59, 59, 59, 59, 59, 59 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..69.

EXAMPLE

a(2)=7 counts the numbers 3, 5, 7, 11, 13, 17, 19 below 23=A007510(2).

MAPLE

isA007510 := proc(n) RETURN(isprime(n) and not isprime(n-2) and not isprime(n+2)) ; end:

isA001097 := proc(n) RETURN(isprime(n) and (isprime(n-2) or isprime(n+2)) ) ; end:

A007510 := proc(n) local a; if n = 1 then 2; else for a from procname(n-1)+1 do if isA007510(a) then RETURN(a) ; fi; od: fi; end:

A162308 := proc(n) local a, k; a := 0 ; for k from 3 to A007510(n)-1 do if isA001097(k) then a := a+1; fi; od; a; end:

seq(A162308(n), n=1..120) ; # R. J. Mathar, Jul 02 2009

CROSSREFS

Cf. A000040, A073425.

Sequence in context: A058483 A176326 A283056 * A191883 A108815 A262536

Adjacent sequences:  A162305 A162306 A162307 * A162309 A162310 A162311

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Jul 01 2009

EXTENSIONS

Edited by R. J. Mathar, Jul 02 2009

STATUS

approved

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Last modified December 8 04:46 EST 2019. Contains 329853 sequences. (Running on oeis4.)