A189986 Numbers of the form 4k+1 having exactly 4 divisors.

21, 33, 57, 65, 69, 77, 85, 93, 125, 129, 133, 141, 145, 161, 177, 185, 201, 205, 209, 213, 217, 221, 237, 249, 253, 265, 301, 305, 309, 321, 329, 341, 365, 377, 381, 393, 413, 417, 437, 445, 453, 469, 473, 481, 485, 489, 493, 497, 501, 505, 517, 533, 537, 545

Offset: 1

Author

Juri-Stepan Gerasimov, May 03 2011

Keywords

• nonn

Comments

Intersection of A016813 and A030513; subsequence of A007422.

Numbers p*q with p == q (mod 4) together with p^3 with p == 1 (mod 4), p and q distinct primes. - Charles R Greathouse IV, May 03 2011

Links

• G. C. Greubel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A007422, A016813, A030513.

Programs

Magma

[ n: n in [1..600 by 4] | #Divisors(n) eq 4 ]; // Klaus Brockhaus, May 04 2011

Mathematica

Select[4Range[200]+1,DivisorSigma[0,#]==4&] (* Harvey P. Dale, May 11 2011 *)

Extensions

Corrected (497 inserted) by Klaus Brockhaus, May 04 2011