cp's OEIS Frontend

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.

A097319 Numbers with more than one prime factor and, in the ordered factorization, the exponents are strictly increasing.

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%I A097319 #24 Feb 23 2024 07:28:32
%S A097319 18,50,54,75,98,108,147,162,242,245,250,324,338,363,375,486,500,507,
%T A097319 578,605,648,686,722,845,847,867,972,1029,1058,1083,1125,1183,1250,
%U A097319 1372,1445,1458,1587,1682,1715,1805,1859,1875,1922,1944,2023,2250
%N A097319 Numbers with more than one prime factor and, in the ordered factorization, the exponents are strictly increasing.
%C A097319 If n = Product[k=1..m, p(k)^e(k)], then m>1 and e(1) < e(2) <...< e(m).
%H A097319 T. D. Noe, <a href="/A097319/b097319.txt">Table of n, a(n) for n = 1..1180</a>
%e A097319 507 is 3^1*13^2, A001221(507)=2 and 1<2, so 507 is in sequence.
%e A097319 150 is 2^1*3^1*5^2 is not in the sequence because 1,1,2 is not strictly increasing (although it is nondecreasing).
%t A097319 fQ[n_] := Module[{d, f = FactorInteger[n]}, If[Length[f] == 1, False, d = Differences[Transpose[f][[2]]]; And @@ ((# > 0) & /@ d)]]; Select[Range[2250], fQ] (* _T. D. Noe_, Apr 09 2013 *)
%o A097319 (PARI) for(n=1, 3000, F=factor(n); t=0; s=matsize(F)[1]; if(s>1, for(k=1, s-1, if(F[k, 2]>=F[k+1, 2], t=1; break)); if(!t, print1(n", "))))
%o A097319 (PARI) is(n) = my(f = factor(n)[,2]); #f > 1 && vecsort(f, , 8) == f \\ _Rick L. Shepherd_, Jan 17 2018
%Y A097319 Subset of A126706. Cf. A097318, A097320.
%K A097319 nonn
%O A097319 1,1
%A A097319 _Ralf Stephan_, Aug 04 2004