OFFSET
1,2
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..64
Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).
MATHEMATICA
lucasQ[n_] := Or @@ (IntegerQ[Sqrt[#]] & /@ (5*n^2 + 20*{-1, 1})); Select[Range[10^4], lucasQ[EulerPhi[#]] &] (* Amiram Eldar, May 27 2024 *)
PROG
(Python)
from sympy.ntheory.primetest import is_square
from sympy import totient
islucas = lambda n: is_square(5*n*n - 20) or is_square(5*n*n + 20)
print([n for n in range(1, 10**4) if islucas(totient(n))])
(PARI) isok(k) = islucas(eulerphi(k)); \\ using islucas from A102460 \\ Michel Marcus, May 27 2024
(PARI) \\ read Max Alekseyev's invphi.gp
a373194(uptoNLucas) = my(A=List()); for(n=0, uptoNLucas, my(L = invphi(fibonacci(n+1) + fibonacci(n-1))); if(#L, for(k=1, #L, listput(A, L[k])))); Set(A);
a373194(150) \\ Hugo Pfoertner, Jun 10 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Darío Clavijo, May 27 2024
EXTENSIONS
a(18)-a(21) from Amiram Eldar, May 27 2024
a(22) onwards from Hugo Pfoertner, May 27 2024
STATUS
approved