OFFSET
1,1
COMMENTS
Also terms of A014574 such that twice the term is also in A014574. Related to a problem of anti-divisors.
A117499(a(n)) = 4. - Reinhard Zumkeller, Mar 23 2006
All a(n) > 6 must be a multiple of 30: As for elements of A014574, we must have a(n) = 6k, and k = 5m+-1 would lead to a(n)-+1 divisible by 5, while k = 5m+-2 would lead to 2*a(n)+-1 divisible by 5, so only k=5m is possible. - M. F. Hasler, Nov 27 2010
LINKS
Harry J. Smith, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Bitwin Chain
EXAMPLE
For n=30, 29 and 31 are prime, as are 59 and 61.
MATHEMATICA
lst={}; Do[p1=Prime[n]; p2=Prime[n+1]; d=2; If[p2-p1==d, w=p1+1; If[PrimeQ[2*w-1]&&PrimeQ[2*w+1], AppendTo[lst, w]]], {n, 1, 10^4}]; lst (* Vladimir Joseph Stephan Orlovsky, Aug 07 2008 *)
PROG
(PARI) { n=0; forstep (m=2, 10^9, 2, if (isprime(m - 1) && isprime(m + 1) && isprime(2*m - 1) && isprime(2*m + 1), write("b066388.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Feb 13 2010
CROSSREFS
KEYWORD
nonn
AUTHOR
Jud McCranie, Dec 23 2001
STATUS
approved