OFFSET
1,2
COMMENTS
The bi-unitary totient function of numbers k such that k and k+1 have the same function value (A293184).
EXAMPLE
9 is in the sequence since 9 = bphi(14) = bphi(15).
MATHEMATICA
bphi[1] = 1; bphi[n_] := With[{pp = Power @@@ FactorInteger[n]}, Count[Range[n], m_ /; Intersection[pp, Power @@@ FactorInteger[m]] == {}]]; a={}; b1=0; Do[b2 = bphi[k]; If[b1 == b2, a = AppendTo[a, b1]]; b1 = b2, {k, 1, 10^2}]; a (* after Jean-François Alcover at A116550 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Oct 22 2017
EXTENSIONS
a(10)-a(11) from Michel Marcus, Nov 14 2017
a(12)-a(21) from Amiram Eldar, Jul 16 2022
STATUS
approved