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

%I

%S 21,33,57,65,69,77,85,93,125,129,133,141,145,161,177,185,201,205,209,

%T 213,217,221,237,249,253,265,301,305,309,321,329,341,365,377,381,393,

%U 413,417,437,445,453,469,473,481,485,489,493,497,501,505,517,533,537,545

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

%C Intersection of A016813 and A030513; subsequence of A007422.

%C 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 G. C. Greubel, <a href="/A189986/b189986.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[4Range[200]+1,DivisorSigma[0,#]==4&] (* _Harvey P. Dale_, May 11 2011 *)

%o (MAGMA) [ n: n in [1..600 by 4] | #Divisors(n) eq 4 ]; // _Klaus Brockhaus_, May 04 2011

%Y Cf. A007422, A016813, A030513.

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, May 03 2011

%E Corrected (497 inserted) by _Klaus Brockhaus_, May 04 2011

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Last modified July 27 18:27 EDT 2021. Contains 346308 sequences. (Running on oeis4.)