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A211876
Primes of the form Phi(phi(k),2), the phi(k)-th cyclotomic polynomial evaluated at 2, where phi is the Euler totient function.
0
3, 5, 11, 13, 17, 241, 257, 331, 683, 5419, 61681, 65537, 2796203, 15790321, 22366891, 4278255361, 4562284561, 77158673929, 1133836730401, 18446744069414584321, 291280009243618888211558641, 78919881726271091143763623681, 84159375948762099254554456081, 84179842077657862011867889681
OFFSET
1,1
MATHEMATICA
s = Union[Table[EulerPhi[n], {n, 2000}]]; t = Union[Select[Table[ Cyclotomic[ n, 2], {n, s}], PrimeQ]]; Select[t, # < 10^30 &]
PROG
(PARI)
s=Set([]);
for (n=1, 10^3, my(a=polcyclo(eulerphi(n), 2)); if(ispseudoprime(a), s=setunion(s, [a])));
v211876=s /* Joerg Arndt, Apr 13 2013 */
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Gruber, Feb 12 2013
STATUS
approved