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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..24.

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

Cf. A000010, A211875, A211874.

Sequence in context: A243627 A178604 A153443 * A066587 A047621 A239636

Adjacent sequences:  A211873 A211874 A211875 * A211877 A211878 A211879

KEYWORD

nonn

AUTHOR

Alexander Gruber, Feb 12 2013

STATUS

approved

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Last modified October 19 22:55 EDT 2019. Contains 328244 sequences. (Running on oeis4.)