A258436 - OEIS

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

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OFFSET

1,1

COMMENTS

Intersection of A252021 and A258435.

LINKS

Table of n, a(n) for n=1..23.

MATHEMATICA

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

PROG

(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

CROSSREFS

Cf. A252021, A258435.

Sequence in context: A337427 A142766 A326442 * A167992 A038493 A212237

Adjacent sequences: A258433 A258434 A258435 * A258437 A258438 A258439

KEYWORD

nonn,easy

AUTHOR

Carlos Eduardo Olivieri, May 30 2015

STATUS

approved