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 A378541 #11 Dec 03 2024 11:46:01 %S A378541 6,12,20,24,28,30,40,42,48,54,56,60,66,78,80,84,88,90,96,104,108,112, %T A378541 120,126,132,140,150,156,160,168,176,180,192,198,204,208,210,216,220, %U A378541 224,228,234,240,252,260,264,270,272,276,280,294,300,304,306,308,312,320,330,336,340,342,348,352,360,364,368,378,380 %N A378541 Practical numbers whose sum of divisors is even. %C A378541 Practical numbers without any squares or twice squares. %H A378541 Antti Karttunen, <a href="/A378541/b378541.txt">Table of n, a(n) for n = 1..10000</a> %e A378541 20 is in the sequence as it is practical (every number from 1 through sigma(20) = 42 can be written as the sum of some distinct divisors of 20) and sigma(20) = 42 is even. %e A378541 21 is not in the sequence as it is not practical. %o A378541 (PARI) isA378541 = A378540; %Y A378541 Intersection of A005153 and A028983. %Y A378541 Setwise difference A083207 \ A353061. %Y A378541 Cf. A378540 (characteristic function). %K A378541 nonn %O A378541 1,1 %A A378541 _Antti Karttunen_ and _David A. Corneth_, Dec 02 2024