

A074973


Smallest index i such that next_prime( 2*prime(i) )  2*prime(i) = 2n  1.


0



1, 4, 11, 20, 17, 67, 104, 56, 125, 165, 182, 316, 236, 359, 407, 1254, 667, 836, 1521, 1210, 1966, 3197, 1520, 2294, 2279, 2046, 5410, 5472, 1965, 6702, 13947, 10138, 12122, 16760, 7659, 22325, 16784, 13072, 36169, 17852, 15414, 69872, 23814, 16370, 46752
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OFFSET

1,2


COMMENTS

First index i such that NextPrime[p2=2*Prime[i]]p2 is 2n1; case n=1 corresponds to Sophie Germain (SG) primes, others may be called SG nprimes. Distance between 2*(nth prime) and next prime in A059787.


LINKS

Table of n, a(n) for n=1..45.


EXAMPLE

a(54) = 342337 because difference between 2*p(342337) and next prime is 2*54 1 = 107 and 342337 is the smallest such index.


PROG

(PARI) a(n) = {i = 1; while (nextprime(p2=2*prime(i))  p2 != 2*n1, i++); i; } \\ Michel Marcus, Oct 03 2013
(MAGMA)
S:=[];
i:=1;
for n in [1..45] do
while not NextPrime(2*NthPrime(i))2*NthPrime(i) eq 2*n1 do
i:=i+1;
end while;
Append(~S, i);
i:=1;
end for;
S; // Bruno Berselli, Oct 03 2013


CROSSREFS

Cf. A059787.
Sequence in context: A009908 A321643 A049935 * A327457 A025526 A301093
Adjacent sequences: A074970 A074971 A074972 * A074974 A074975 A074976


KEYWORD

nonn


AUTHOR

Zak Seidov, Oct 06 2002


EXTENSIONS

a(44)a(45) from Bruno Berselli, Oct 03 2013


STATUS

approved



