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 A376715 #23 Oct 05 2024 00:39:50 %S A376715 4,8,9,12,16,18,20,25,27,28,32,36,44,45,48,49,50,52,63,64,68,72,75,76, %T A376715 80,81,92,98,99,100,108,112,116,117,121,124,125,128,144,147,148,153, %U A376715 162,164,169,171,172,175,176,180,188,192,196,200,207,208,212,225,236,242,243,244,245 %N A376715 Composite numbers in A265640. %C A376715 The first dozen terms match those of A013929; 40 is the smallest number that is not squarefree and therefore in A013929 but whose prime factors cannot be artranged to form a palindrome. Other examples are 54, 56, and 60. On the other hand, the current sequence is a proper subset of both A013929 and A265640. %C A376715 Note that, like A265640, this is not a base-dependent sequence. %H A376715 Michael S. Branicky, <a href="/A376715/b376715.txt">Table of n, a(n) for n = 1..10000</a> %e A376715 44 is a term, since 44 = 2*11*2. %e A376715 52 is a term, since 52 = 2*13*2. %e A376715 180 is a term, since 180 = 2*3*5*3*2. %e A376715 676 is a term, since 676 = 2*13*13*2. %o A376715 (PARI) isok(n)=my(f=factor(n)[,2]); vecsum(f)>=2 && #select(e->e%2, f)<=1 \\ _Andrew Howroyd_, Oct 02 2024 %o A376715 (Python) %o A376715 from math import isqrt %o A376715 from sympy.ntheory.factor_ import core, isprime %o A376715 def ok(n): return n > 3 and (isqrt(n)**2 == n or (not isprime(n) and isprime(core(n)))) %o A376715 print([k for k in range(1, 246) if ok(k)]) # _Michael S. Branicky_, Oct 03 2024 %Y A376715 Intersection of A002808 and A265640. %Y A376715 Cf. A013929, A265640. %K A376715 nonn,base %O A376715 1,1 %A A376715 _Marc Groz_, Oct 02 2024