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 A235524 #15 Jan 19 2014 00:32:48 %S A235524 1,2,8,9,12,18,72,80,96,108,128,288,448,625,720,864,972,1152,1200, %T A235524 1250,1620,1944,2000,2025,2560,4032,4050,5000,5625,6144,6561,6912, %U A235524 7500,7776,9408,10800,11250,11264,12960,13122,16200,18000,18432,19440,20412,21952 %N A235524 Primitive refactorable (or tau) numbers: refactorable numbers which are not part of any family. %C A235524 To be "primitive", the set of prime factors of N and of d(N) must be identical, otherwise any prime only in N is arbitrary and this defines a family of refactorable numbers. These are referred to as generators in the Zelinsky reference. %C A235524 This sequence is therefore the intersection of the refactorable numbers (A033950) and those numbers with identical sets of prime factors for N and d(N) (A081381). %C A235524 The first numbers in A081381 which are not in this sequence are 486, 768, 8748, and 303750. This sequence is A235525. %H A235524 Walter Roscello and Giovanni Resta, <a href="/A235524/b235524.txt">Table of n, a(n) for n = 1..1008</a> (terms < 10^11, first 459 terms from Walter Roscello) %H A235524 Joshua Zelinsky, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL5/Zelinsky/zelinsky9.html">Tau Numbers: A Partial Proof of a Conjecture and Other Results</a>, Journal of Integer Sequences, Vol. 5 (2002), Article 02.2.8 %e A235524 720 is in the sequence since 720 = 2^4 * 3^2 * 5^1, therefore the prime decomposition of d(720) is 5 * 3 * 2 and each prime in 720 is required to make it refactorable. %Y A235524 Cf. A000005, A033950, A081381, A235525. %K A235524 nonn,easy %O A235524 1,2 %A A235524 _Walter Roscello_, Jan 11 2014