OFFSET
1,1
COMMENTS
An equivalent definition of this sequence: 5 together with primes p such that p == -1 (mod 30) and 2*p + 1 is also prime.
These numbers do not occur in A137715.
From Arkadiusz Wesolowski, Aug 25 2012: (Start)
The sequence contains numbers like 1409 which are in A053027.
a(n) is in A002515 if and only if a(n) is congruent to -1 mod 60. (End)
LINKS
Arkadiusz Wesolowski, Table of n, a(n) for n = 1..10000
C. K. Caldwell, "Top Twenty" page, Lucas cofactor
Eric Weisstein's World of Mathematics, Lucas Number
EXAMPLE
29 is in the sequence since it is prime and 59 is a factor of Lucas(29) = 1149851.
MATHEMATICA
Select[Prime@Range[740], Divisible[LucasL[#], 2*# + 1] &]
Prepend[Select[Range[29, 5639, 30], PrimeQ[#] && PrimeQ[2*# + 1] &], 5]
PROG
(Magma) [5] cat [n: n in [29..5639 by 30] | IsPrime(n) and IsPrime(2*n+1)];
(PARI) is_A215850(n)=isprime(n)&!real((Mod(2, 2*n+1)+quadgen(5))*quadgen(5)^n) \\ - M. F. Hasler, Aug 25 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Arkadiusz Wesolowski, Aug 24 2012
STATUS
approved