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A131574 Numbers n that are the product of two distinct odd primes and x^2 + y^2 = n has integer solutions. 9
65, 85, 145, 185, 205, 221, 265, 305, 365, 377, 445, 481, 485, 493, 505, 533, 545, 565, 629, 685, 689, 697, 745, 785, 793, 865, 901, 905, 949, 965, 985, 1037, 1073, 1145, 1157, 1165, 1189, 1205, 1241, 1261, 1285, 1313, 1345, 1385, 1405, 1417, 1465, 1469 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The two primes are of the form 4*k + 1.

LINKS

Colin Barker, Table of n, a(n) for n = 1..1000

EXAMPLE

65 is in the sequence because x^2 + y^2 = 65 = 5*13 has solutions (x,y) = (1,8), (4,7), (7,4) and (8,1).

PROG

(PARI)

dop(d, nmax) = {

  my(L=List(), v=vector(d, m, 1)~, f);

  for(n=1, nmax,

    f=factorint(n);

    if(#f~==d && f[1, 1]>2 && f[, 2]==v && f[, 1]%4==v, listput(L, n))

  );

  Vec(L)

}

dop(2, 3000) \\ Colin Barker, Nov 15 2015

CROSSREFS

Cf. A000415, A121387, A248649, A248712, A264498, A264499

Sequence in context: A224770 A274044 A024409 * A323272 A322781 A020273

Adjacent sequences:  A131571 A131572 A131573 * A131575 A131576 A131577

KEYWORD

nonn

AUTHOR

Colin Barker, Aug 28 2007, corrected Aug 29 2007

STATUS

approved

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Last modified April 22 10:17 EDT 2019. Contains 322330 sequences. (Running on oeis4.)