

A162308


Number of twin primes A001097 smaller than the nontwin 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(n2) and not isprime(n+2)) ; end:
isA001097 := proc(n) RETURN(isprime(n) and (isprime(n2) or isprime(n+2)) ) ; end:
A007510 := proc(n) local a; if n = 1 then 2; else for a from procname(n1)+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

JuriStepan Gerasimov, Jul 01 2009


EXTENSIONS

Edited by R. J. Mathar, Jul 02 2009


STATUS

approved



