A068367 Numbers k such that phi(k)^2+sigma(k)^2 is prime.

1, 4, 8, 25, 50, 121, 225, 324, 400, 800, 1024, 1250, 1681, 1682, 2025, 2209, 4761, 5041, 5625, 6561, 6724, 7569, 11449, 17424, 18225, 18769, 21609, 26244, 34969, 36481, 38809, 42050, 59858, 62001, 72900, 90000, 102152, 108900

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..5000

Mathematica

Select[Range[110000], PrimeQ[EulerPhi[#]^2+DivisorSigma[1, #]^2]&] (* Harvey P. Dale, Jul 21 2019 *)

Prog

(PARI) isok(k) = {my(f = factor(k)); isprime(eulerphi(f)^2 + sigma(f)^2); } \\ Amiram Eldar, Apr 25 2025

Crossrefs

Cf. A000010 (phi), A000203 (sigma).

Sequence in context: A154586 A371190 A185615 * A292548 A000964 A297458

Adjacent sequences: A068364 A068365 A068366 * A068368 A068369 A068370

Keyword

nonn

Author

Benoit Cloitre, Feb 28 2002

Status

approved