OFFSET
1,4
COMMENTS
(Sum_{n=1..N} k) / (Sum_{n=1..N} log(p)^2) tends to 1 as N increases.
LINKS
Pierre CAMI, Table of n, a(n) for n = 1..10000
EXAMPLE
1*2*(1*2 + 1) - 1 = 5 and 1*2*(1*2 + 1) + 1 = 7;
5 and 7 are twin primes, so a(1)=1 as p(1)=2.
1*3*(1*3 + 1) - 1 = 11 and 1*3*(1*3 + 1) + 1 = 13;
11 and 13 are twin primes, so a(2)=1 as p(2)=3.
MAPLE
A200654 := proc(n)
p := ithprime(n) ;
for k from 1 do
if isprime(k*p*(k*p+1)-1) and isprime(k*p*(k*p+1)+1) then
return k;
end if;
end do:
return 0 ;
end proc:
seq(A200654(n), n=1..80) ; # R. J. Mathar, Nov 26 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Nov 20 2011
STATUS
approved