OFFSET
1,1
LINKS
M. F. Hasler, Table of n, a(n) for n = 1..4911 (all terms up to 5*10^5).
EXAMPLE
29 is in the sequence since there are no primes in the interval(4*29,4*31)=(116,124)
MATHEMATICA
Select[Prime[Range[500]], Count[Range[4*#, 4*NextPrime[#]], _?PrimeQ]==0&] (* Harvey P. Dale, Jan 05 2013 *)
PROG
(PARI) is_A218561(p)=isprime(p)&nextprime(4*p)>=4*nextprime(p+1) \\ - M. F. Hasler, Nov 03 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev and Peter J. C. Moses, Nov 02 2012
STATUS
approved