A326403 Numbers k such that iphi(k) = iphi(k+1), where iphi(k) is an infinitary analog to the Euler totient function (A091732).

1, 20, 35, 143, 194, 208, 740, 1220, 1299, 1419, 1803, 1892, 3705, 3716, 3843, 5186, 5635, 7868, 10659, 13634, 13905, 17948, 18507, 18914, 18980, 21007, 25388, 25545, 30380, 31599, 32304, 34595, 37820, 47067, 70394, 73059, 78064, 87856, 94874, 105908, 116963

Offset

1,2

Links

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

Example

20 is in the sequence since iphi(20) = iphi(21) = 12.

Mathematica

f[p_, e_] := p^(2^(-1 + Position[Reverse @ IntegerDigits[e, 2], _?(# == 1 &)])); a[1] = 1; a[n_] := Times @@ (Flatten @(f @@@ FactorInteger[n]) - 1); a1 = 1; s = {}; Do[a2 = a[n]; If[a1 == a2, AppendTo[s, n - 1]]; a1 = a2, {n, 2, 10^5}]; s

Crossrefs

Cf. A001274, A091732, A287055, A293184, A301866.

Sequence in context: A384493 A048066 A287055 * A335251 A135801 A396126

Adjacent sequences: A326400 A326401 A326402 * A326404 A326405 A326406

Keyword

nonn

Author

Amiram Eldar, Sep 14 2019

Status

approved