OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
2*3+1 = 5, 2*5+1 = 7, 2*7 - 1 = 13; 3, 5 and 7 are consecutive primes as are 5, 7 and 13, so a(1) = 2 as 3 = prime(2).
MATHEMATICA
s={}; n=1; p1=2; p2=3; Do[p3 = NextPrime[p2]; If[PrimeQ[2*p1+1] && (np = NextPrime[2*p1+1]) == 2*p2+1 && NextPrime[np] == 2*p3-1, AppendTo[s, n]]; p1=p2; p2=p3; n++, {10^5}]; s (* Amiram Eldar, Jul 23 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Feb 18 2005
EXTENSIONS
Corrected by T. D. Noe, Nov 02 2006
a(21) and a(30) inserted and a(36) added by Amiram Eldar, Jul 23 2021
STATUS
approved