This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A189986 #22 Jun 27 2024 22:15:43 %S A189986 21,33,57,65,69,77,85,93,125,129,133,141,145,161,177,185,201,205,209, %T A189986 213,217,221,237,249,253,265,301,305,309,321,329,341,365,377,381,393, %U A189986 413,417,437,445,453,469,473,481,485,489,493,497,501,505,517,533,537,545 %N A189986 Numbers of the form 4k+1 having exactly 4 divisors. %C A189986 Intersection of A016813 and A030513; subsequence of A007422. %C A189986 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 %H A189986 G. C. Greubel, <a href="/A189986/b189986.txt">Table of n, a(n) for n = 1..10000</a> %t A189986 Select[4Range[200]+1,DivisorSigma[0,#]==4&] (* _Harvey P. Dale_, May 11 2011 *) %o A189986 (Magma) [ n: n in [1..600 by 4] | #Divisors(n) eq 4 ]; // _Klaus Brockhaus_, May 04 2011 %Y A189986 Cf. A007422, A016813, A030513. %K A189986 nonn %O A189986 1,1 %A A189986 _Juri-Stepan Gerasimov_, May 03 2011 %E A189986 Corrected (497 inserted) by _Klaus Brockhaus_, May 04 2011