A258436 Primes p of form x^2 - phi(x) such that (p-1)/tau(p-1) is also prime.

157, 1069, 61837, 190573, 840109, 1950349, 2485453, 20616397, 38844349, 57648589, 133091053, 144685357, 188582029, 222029869, 276773389, 346282477, 399067213, 472656589, 827175949, 929558797, 1137622957, 1352220109, 1369037389

Offset: 1

Author

Carlos Eduardo Olivieri, May 30 2015

Keywords

• nonn
• easy

Comments

Intersection of A252021 and A258435.

Crossrefs

Cf. A252021, A258435.

Programs

Mathematica

lst = Table[n^2 - EulerPhi[n], {n, 100000}]; Select[lst, PrimeQ[#] && PrimeQ[ ( # - 1)/DivisorSigma[0, # - 1] ] &]

PARI

lista(nn) = {for (n=1, nn, if (isprime(p=n^2-eulerphi(n)) && (pp=p-1) && (type(r=pp/numdiv(pp))=="t_INT") && isprime(r), print1(p, ", ")););} \\ Michel Marcus, Jul 08 2015