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 A345211 #10 Oct 11 2023 03:54:20 %S A345211 2,4,6,10,14,18,20,22,26,28,30,34,38,42,44,46,50,52,54,58,62,66,68,70, %T A345211 74,76,78,82,86,90,92,94,98,100,102,106,110,114,116,118,122,124,126, %U A345211 130,134,138,140,142,146,148,150,154,158,162,164,166,170,172,174,178,182,186,188 %N A345211 Numbers with the same number of odd / even, refactorable divisors. %C A345211 All the terms are even. Conjecture: The sequence a(n)/2 is the complement of A157932 (verified for a(n) < 4*10^7). - _Amiram Eldar_, Oct 11 2023 %H A345211 Amiram Eldar, <a href="/A345211/b345211.txt">Table of n, a(n) for n = 1..10000</a> %e A345211 18 is in the sequence since it has 2 odd and 2 even, refactorable divisors: 1, 2, 9, and 18. %t A345211 q[n_] := DivisorSum[n, (-1)^# &, Divisible[#, DivisorSigma[0, #]] &] == 0; Select[Range[2, 200, 2], q] (* _Amiram Eldar_, Oct 11 2023 *) %o A345211 (PARI) is(n) = (n%2)! && sumdiv(n, d, (-1)^d * !(d % numdiv(d))) == 0; \\ _Amiram Eldar_, Oct 11 2023 %Y A345211 Cf. A033950, A157932, A336041. %K A345211 nonn %O A345211 1,1 %A A345211 _Wesley Ivan Hurt_, Jun 10 2021