cp's OEIS Frontend

A360358 Numbers k such that A360327(k) = A360327(k+1) > 1.

%I A360358 #9 Feb 06 2023 01:28:18
%S A360358 714,6603,16115,18920,23154,24530,39984,41360,42789,51204,56814,58190,
%T A360358 59619,60995,65229,66605,68034,69410,73644,79304,82059,84249,84864,
%U A360358 86240,94655,101375,101694,103070,107304,108680,121374,125510,126125,126939,135128,135354,137329
%N A360358 Numbers k such that A360327(k) = A360327(k+1) > 1.
%C A360358 Numbers k such that A360327(k) = A360327(k+1) = 1 are terms of A360357.
%H A360358 Amiram Eldar, <a href="/A360358/b360358.txt">Table of n, a(n) for n = 1..10000</a>
%e A360358 714 is a term since A360327(714) = A360327(715) = 72 > 1.
%t A360358 f[p_, e_] := If[PrimeQ[PrimePi[p]], (p^(e+1)-1)/(p-1), 1]; s[1] = 1; s[n_] := Times @@ f @@@ FactorInteger[n]; seq = {}; s1 = s[1]; n = 2; c = 0; While[c < 40, s2 = s[n]; If[s1 == s2 > 1, c++; AppendTo[seq, n - 1]]; s1 = s2; n++]; seq
%o A360358 (PARI) s(n) = {my(f = factor(n), p = f[,1], e = f[,2]); prod(i = 1, #p, if(isprime(primepi(p[i])), (p[i]^(e[i]+1)-1)/(p[i]-1), 1));}
%o A360358 lista(nmax) = {my(s1 = s(1), s2); for(n=2, nmax, s2=s(n); if(s2 > 1 && s1 == s2, print1(n-1, ", ")); s1 = s2); }
%Y A360358 Cf. A360327, A360357.
%Y A360358 Similar sequences: A002961, A064115, A064125, A293183, A306985, A360359.
%K A360358 nonn
%O A360358 1,1
%A A360358 _Amiram Eldar_, Feb 04 2023