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 A181800 #28 Apr 18 2025 20:58:42
%S A181800 1,4,8,16,32,36,64,72,128,144,216,256,288,432,512,576,864,900,1024,
%T A181800 1152,1296,1728,1800,2048,2304,2592,3456,3600,4096,4608,5184,5400,
%U A181800 6912,7200,7776,8192,9216,10368,10800,13824,14400,15552,16384,18432,20736,21600,27000
%N A181800 Powerful numbers that are the least integer of their prime signature.
%C A181800 Apart from 1, all terms in this sequence are multiples of 4. - _Charles R Greathouse IV_, Dec 13 2016
%C A181800 Apart from 1, the prime factor exponents of the terms in this sequence represent exactly every factorization of every integer k >= 2. E.g. the two factorizations of 4 are represented by 16 (2^4 -> {4}) and 36 (2^2 * 3^2 -> {2, 2}; 2 * 2 = 4). The smallest such term for each k is subsequence A085629. - _Charles L. Hohn_, Apr 04 2025
%H A181800 Amiram Eldar, <a href="/A181800/b181800.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Charles R Greathouse IV)
%F A181800 Intersection of A001694 and A025487.
%o A181800 (PARI) is(n)=if(n<4,return(n==1)); my(f=factor(n)); vecmin(f[,2])>1 && f[,1]~ == primes(#f~) && f[,2] == vecsort(f[,2],,4) \\ _Charles R Greathouse IV_, Sep 14 2015
%Y A181800 Cf. A001694 (powerful numbers), A025487 (least integer of each prime signature).
%Y A181800 Cf. A085629.
%K A181800 nonn
%O A181800 1,2
%A A181800 _Matthew Vandermast_, Dec 02 2010