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 A359161 #6 Dec 17 2022 20:03:19 %S A359161 1,9,21,25,33,49,57,65,69,77,81,85,93,121,129,133,141,145,161,169,177, %T A359161 185,189,201,205,209,213,217,221,225,237,249,253,265,289,297,301,305, %U A359161 309,321,329,341,361,365,377,381,393,413,417,437,441,445,453,469,473,481,485,489,493,497,501,505,513 %N A359161 Numbers of the form 4u+1 with an even number of prime factors (counted with multiplicity). %o A359161 (PARI) isA359161(n) = A359160(n); %Y A359161 Intersection of A016813 and A028260. %Y A359161 Setwise difference A046337 \ A359163. %Y A359161 Setwise difference A016813 \ A359151. %Y A359161 Cf. A108181 (subsequence). %Y A359161 Cf. A359160 (characteristic function). %K A359161 nonn %O A359161 1,2 %A A359161 _Antti Karttunen_, Dec 17 2022