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.

A316476 Stable numbers. Numbers whose distinct prime indices are pairwise indivisible.

This page as a plain text file.
%I A316476 #14 Nov 27 2024 17:57:04
%S A316476 1,2,3,4,5,7,8,9,11,13,15,16,17,19,23,25,27,29,31,32,33,35,37,41,43,
%T A316476 45,47,49,51,53,55,59,61,64,67,69,71,73,75,77,79,81,83,85,89,91,93,95,
%U A316476 97,99,101,103,107,109,113,119,121,123,125,127,128,131,135,137
%N A316476 Stable numbers. Numbers whose distinct prime indices are pairwise indivisible.
%C A316476 A prime index of n is a number m such that prime(m) divides n.
%H A316476 Andrew Howroyd, <a href="/A316476/b316476.txt">Table of n, a(n) for n = 1..10000</a>
%H A316476 <a href="/index/Pri#prime_indices">Index entries for sequences related to prime indices in the factorization of n</a>
%e A316476 The prime indices of 45 are {2,2,3}, so the distinct prime indices are {2,3}, which are pairwise indivisible, so 45 belongs to the sequence.
%e A316476 The prime indices of 105 are {2,3,4}, which are not pairwise indivisible (2 divides 4), so 105 does not belong to the sequence.
%t A316476 Select[Range[100],Select[Tuples[If[#===1,{},Cases[FactorInteger[#],{p_,k_}:>PrimePi[p]]],2],UnsameQ@@#&&Divisible@@#&]=={}&]
%o A316476 (PARI) ok(n)={my(v=apply(primepi, factor(n)[,1])); for(j=2, #v, for(i=1, j-1, if(v[j]%v[i]==0, return(0)))); 1} \\ _Andrew Howroyd_, Aug 26 2018
%Y A316476 Cf. A056239, A112798, A285572, A285573, A303362, A304713, A316468, A316475, A327393, A327394, A378442 (characteristic function).
%K A316476 nonn
%O A316476 1,2
%A A316476 _Gus Wiseman_, Jul 04 2018