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 A189986 Numbers of the form 4k+1 having exactly 4 divisors. 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 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 MATHEMATICA Select[4Range[200]+1, DivisorSigma[0, #]==4&] (* Harvey P. Dale, May 11 2011 *) PROG (MAGMA) [ n: n in [1..600 by 4] | #Divisors(n) eq 4 ]; // Klaus Brockhaus, May 04 2011 CROSSREFS Cf. A007422, A016813, A030513. Sequence in context: A176945 A333857 A070006 * A190299 A280262 A084109 Adjacent sequences:  A189983 A189984 A189985 * A189987 A189988 A189989 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, May 03 2011 EXTENSIONS Corrected (497 inserted) by Klaus Brockhaus, May 04 2011 STATUS approved

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Last modified June 14 15:36 EDT 2021. Contains 345025 sequences. (Running on oeis4.)