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.

A360129 Numbers k such that A360119(k) > 1, but which have no divisors d > 1 such that d+1 is also a divisor.

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%I A360129 #6 Feb 21 2023 07:35:14
%S A360129 572,1144,1292,1768,2288,2584,2590,3496,3596,4030,4576,4930,6292,6992,
%T A360129 7052,7192,7436,8050,8170,8246,9044,9152,9212,9430,9724,9758,10868,
%U A360129 11408,12136,12584,12950,13984,14104,14212,14384,14396,14872,15370,16168,16492,16588,16796,17066,17168,17732,18130,18304
%N A360129 Numbers k such that A360119(k) > 1, but which have no divisors d > 1 such that d+1 is also a divisor.
%F A360129 {k | A088722(k) = 0 and A360119(k) > 1}.
%o A360129 (PARI)
%o A360129 A360119(n) = { my(d=divisors(n), erot=vecsort(vector(#d-1, k, d[k+1] - d[k])), s=#d); for(i=1,#erot,if(n%erot[i], s--, if(1==i || erot[i]!=erot[i-1], s--))); (s); };
%o A360129 A360128(n) = !sumdiv(n,d,(d>1)&&!(n%(d+1)));
%o A360129 isA360129(n) = (A360128(n)&&(A360119(n)>1));
%Y A360129 Subsequence of A088725.
%Y A360129 Cf. A088722, A360119, A360128.
%K A360129 nonn
%O A360129 1,1
%A A360129 _Antti Karttunen_, Feb 20 2023