A124983 Nonprime numbers == 1 (mod 4) with a unique partition as a sum of 2 squares x^2 + y^2.

1, 9, 45, 49, 81, 117, 121, 153, 245, 261, 333, 361, 369, 405, 441, 477, 529, 549, 605, 637, 657, 729, 801, 833, 873, 909, 961, 981, 1017, 1053, 1089, 1233, 1341, 1377, 1413, 1421, 1557, 1573, 1629, 1737, 1773, 1805, 1813, 1849, 2009, 2057, 2061, 2097, 2169

Offset: 1

Author

Artur Jasinski, Nov 16 2006

Keywords

• nonn

Comments

Intersection of A124982 and A125018. - Michel Marcus, Nov 02 2013

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000161, A002145, A124982, A125018, A125020.

Programs

Mathematica

Select[4 * Range[0, 500] + 1, !PrimeQ[#] && Length @ PowersRepresentations[#, 2, 2] == 1 &] (* Amiram Eldar, Mar 12 2020 *)

PARI

isok(n)= {if (isprime(n) || (n % 4 != 1), return (0)); A000161(n) == 1;} \\ Michel Marcus, Nov 02 2013

Extensions

More terms from Michel Marcus, Nov 02 2013