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 A247129 Semiprimes n such that phi(n) is a square. 5
 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

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Last modified April 22 02:54 EDT 2024. Contains 371887 sequences. (Running on oeis4.)