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 A178492 #12 Aug 04 2024 17:59:58
%S A178492 1,3,22,70,81,94,115,119,170,214,217,265,310,322,343,364,382,385,400,
%T A178492 472,497,517,527,679,710,742,745,782,820,862,884,889,935,970,1004,
%U A178492 1066,1080,1174,1177,1207,1219,1270,1393,1426,1465,1501,1566,1612,1624,1645
%N A178492 Primitive elements of A006532, i.e., which are not product of earlier terms (> 1) in that sequence.
%C A178492 If a,b are coprime elements of A006532, their product is again in A006532. But there are some a,b which are not coprime and still a,b,a*b are in A006532: First examples are 820*{2860, 3340, 8580, 10020, 11620, ...}.
%H A178492 Donovan Johnson, <a href="/A178492/b178492.txt">Table of n, a(n) for n = 1..10000</a>
%e A178492 The terms a(2)=3 and a(3)=22 are coprime elements of A006532, therefore 3*22=66 is a non-primitive element of A006532, and not listed in this sequence.
%o A178492 (PARI) for(n=1,1e4, issquare(sigma(n))||next; fordiv( n,d, d>1||next; d*d>n & break; issquare(sigma(d)) & issquare(sigma(n/d)) & next(2) ); print1(n","))
%K A178492 nonn
%O A178492 1,2
%A A178492 _Farideh Firoozbakht_ and _M. F. Hasler_, Jun 10 2010