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.
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
Keywords
Programs
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Mathematica
s = Union[Table[EulerPhi[n], {n, 2000}]]; t = Union[Select[Table[ Cyclotomic[ n, 2], {n, s}], PrimeQ]]; Select[t, # < 10^30 &] -
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 */