OFFSET
1,1
COMMENTS
Using Xylouris' version of Linnik's theorem, a(n) << (n/e)^(2.6n). - Charles R Greathouse IV, Dec 22 2011
EXAMPLE
a(7) = 4 because 4*7!! - 1 = 4*105 - 1 = 419 is prime.
MAPLE
A202449 := proc(n)
for k from 1 do
if isprime(k*doublefactorial(n)-1) then
return k;
end if;
end do:
end proc:
seq(A202449(n), n=1..80) ; # R. J. Mathar, Dec 22 2011
MATHEMATICA
Table[k = 0; While[!PrimeQ[k*n!! -1], k++]; k, {n, 85}]
PROG
(PARI) a(n)=my(N=prod(k=1, n\2, 2*k+n%2), k); while(!isprime(k++*N-1), ); k \\ Charles R Greathouse IV, Dec 22 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Dec 19 2011
STATUS
approved