OFFSET
0,2
COMMENTS
Used to prove there are infinitely many primes of the form 4k-1 (see A282705).
REFERENCES
T. M. Apostol, Introduction to Analytic Number Theory, Springer-Verlag, 1976, page 147.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
MAPLE
f:=n->mul(ithprime(i), i=1..n); s1 := [seq(2*f(n)-1, n=0..20)];
MATHEMATICA
Join[{1}, 2 Denominator[Accumulate[1/Prime[Range[20]] - 1]] - 1] (* Vincenzo Librandi, Feb 28 2017 *)
Join[{1}, 2*FoldList[Times, Prime[Range[20]]]-1] (* Harvey P. Dale, Oct 09 2017 *)
PROG
(Magma) [1] cat [2*&*PrimesUpTo(p)-1: p in PrimesUpTo(70)]; // Vincenzo Librandi, Feb 28 2017
(PARI) a(n)=2*prod(i=1, n, prime(i))-1 \\ Charles R Greathouse IV, Feb 28 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Feb 26 2017
STATUS
approved