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 A386245 #7 Jul 20 2025 15:32:01 %S A386245 4,6,22,135,166,444,454,636,650,854,886,1086,1122,1196,1431,1928,2182, %T A386245 2244,2316,2702,3046,3464,3510,3770,4004,4054,4125,4476,4671,5052, %U A386245 5106,5394,5450,6435,6502,6750,8076,8264,8500,9170,9471,9726,10035,10386,10648,10659,11228,11495,11515,11935,12732 %N A386245 Composite numbers k such that A075255(k) is a square. %C A386245 Composite numbers k such that k - sopfr(k) is a square, where sopfr(k) is the sum of prime factors of k with multiplicity. %C A386245 Includes 2*p for p in A056899, but no odd semiprimes. %C A386245 Is this sequence disjoint from A386246? %H A386245 Robert Israel, <a href="/A386245/b386245.txt">Table of n, a(n) for n = 1..10000</a> %e A386245 a(3) = 22 is a term because 22 = 2 * 11 is composite and 22 - (2 + 11) = 9 is a square. %p A386245 filter:= proc(n) local t; %p A386245 if isprime(n) then return false fi; %p A386245 issqr(n - add(t[1]*t[2],t=ifactors(n)[2])) %p A386245 end proc: %p A386245 select(filter, [$4..20000]); %Y A386245 Cf. A056899, A075255, A386246. %K A386245 nonn %O A386245 1,1 %A A386245 _Will Gosnell_ and _Robert Israel_, Jul 16 2025