A360359 Numbers k such that A360331(k) = A360331(k+1).

69, 574, 713, 781, 2394, 2506, 5699, 5750, 6499, 6509, 8441, 19250, 26529, 32130, 36549, 38065, 41749, 41929, 43239, 48025, 50301, 53037, 53382, 59178, 59822, 61754, 66906, 67689, 70277, 71198, 81620, 94000, 100775, 119214, 124640, 127442, 134665, 153202, 154908

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A360331.

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

Sequence in context: A251003 A211692 A264288 * A113707 A259398 A093269

Adjacent sequences: A360356 A360357 A360358 * A360360 A360361 A360362

Keyword

nonn

Author

Amiram Eldar, Feb 04 2023

Status

approved