A360359 - OEIS

%I #10 Feb 06 2023 01:27:53

%S 69,574,713,781,2394,2506,5699,5750,6499,6509,8441,19250,26529,32130,

%T 36549,38065,41749,41929,43239,48025,50301,53037,53382,59178,59822,

%U 61754,66906,67689,70277,71198,81620,94000,100775,119214,124640,127442,134665,153202,154908

%N Numbers k such that A360331(k) = A360331(k+1).

%H Amiram Eldar, <a href="/A360359/b360359.txt">Table of n, a(n) for n = 1..1000</a>

%e 69 is a term since A360331(69) = A360331(70) = 24.

%t f[p_, e_] := If[PrimeQ[PrimePi[p]], 1, (p^(e+1)-1)/(p-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, c++; AppendTo[seq, n - 1]]; s1 = s2; n++]; seq

%o (PARI) s(n) = {my(f = factor(n), p = f[,1], e = f[,2]); prod(i = 1, #p, if(isprime(primepi(p[i])), 1, (p[i]^(e[i]+1)-1)/(p[i]-1)));}

%o lista(nmax) = {my(s1 = s(1), s2); for(n=2, nmax, s2=s(n); if(s1 == s2, print1(n-1, ", ")); s1 = s2); }

%Y Cf. A360331.

%Y Similar sequences: A002961, A064115, A064125, A293183, A306985, A360358.

%K nonn

%O 1,1

%A _Amiram Eldar_, Feb 04 2023