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A247129
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Semiprimes n such that phi(n) is a square.
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5
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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
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OFFSET
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1,1
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COMMENTS
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Freiberg & Pomerance show that this sequence is infinite and a(n) << n^2 log^2 n.
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LINKS
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PROG
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(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)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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