A247129 - OEIS

A247129

Semiprimes n such that phi(n) is a square.

10, 34, 57, 74, 85, 185, 202, 219, 394, 451, 489, 505, 514, 629, 679, 802, 985, 1057, 1154, 1285, 1354, 1387, 1417, 1717, 2005, 2047, 2509, 2594, 2649, 2761, 2885, 3097, 3202, 3277, 3349, 3385, 3409, 3459, 3737, 4207, 4369, 4377, 4577

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

OFFSET

1,1

COMMENTS

Freiberg & Pomerance show that this sequence is infinite and a(n) << n^2 log^2 n.

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Tristan Freiberg, Carl Pomerance, A note on square totients, arXiv:1410.8109 [math.NT], 2014.

PROG

(PARI) is(n)=issquare(eulerphi(n))&&bigomega(n)==2

(PARI) list(lim)=my(v=List()); forprime(p=2, sqrtint(lim\1), forprime(q=p+1, lim\p, if(issquare((p-1)*(q-1)), listput(v, p*q)))); Set(v)

CROSSREFS

Cf. A039770, A221285, A002496.

Sequence in context: A119086 A195900 A322412 * A002601 A020495 A155486

Adjacent sequences: A247126 A247127 A247128 * A247130 A247131 A247132

KEYWORD

nonn

AUTHOR

Charles R Greathouse IV, Nov 19 2014

STATUS

approved