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

714, 6603, 16115, 18920, 23154, 24530, 39984, 41360, 42789, 51204, 56814, 58190, 59619, 60995, 65229, 66605, 68034, 69410, 73644, 79304, 82059, 84249, 84864, 86240, 94655, 101375, 101694, 103070, 107304, 108680, 121374, 125510, 126125, 126939, 135128, 135354, 137329

Offset

1,1

Comments

Numbers k such that A360327(k) = A360327(k+1) = 1 are terms of A360357.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

714 is a term since A360327(714) = A360327(715) = 72 > 1.

Mathematica

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

Prog

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

Crossrefs

Cf. A360327, A360357.

Similar sequences: A002961, A064115, A064125, A293183, A306985, A360359.

Sequence in context: A259674 A321493 A260282 * A166841 A166829 A250378

Adjacent sequences: A360355 A360356 A360357 * A360359 A360360 A360361

Keyword

nonn

Author

Amiram Eldar, Feb 04 2023

Status

approved