OFFSET
1,1
COMMENTS
Limit_{N->oo} (Sum_{n=1..N} k(n)) / (Sum_{n=1..N} log(p(n))^2) = 1.
LINKS
Pierre CAMI, Table of n, a(n) for n = 1..10000
EXAMPLE
2*2*(2*2 - 1) - 1 = 11, twin prime of 13, so a(1)=2.
MAPLE
A200778 := 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:
end proc:
seq(A200778(n), n=1..80) ; # R. J. Mathar, Nov 26 2011
MATHEMATICA
lktpp[n_]:=Module[{k=1, p=Prime[n]}, While[AnyTrue[k*p(k*p-1)+{1, -1}, CompositeQ], k++]; k]; Array[lktpp, 70] (* Harvey P. Dale, May 03 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Nov 22 2011
STATUS
approved