OFFSET
1,2
COMMENTS
a(n) is the Euler totient of A091456(n). Useful for calculating a simple upper bound of the inverse phi function.
LINKS
Nico Mexis, Table of n, a(n) for n = 1..13
John Abbott and Nico Mexis, Cyclotomic Factors and LRS-Degeneracy, arXiv:2403.08751 [math.AC], 2024. See pp. 9, 24.
EXAMPLE
If we know n=276, then all numbers k with phi(k)=n will satisfy k < 5*n since m=a(5) is the first number in the sequence with n < m.
MATHEMATICA
a[n_] := Module[{k = 1, p = 1, e}, While[k <= n*(e = EulerPhi[k]), p = NextPrime[p]; k *= p]; e]; Array[a, 9] (* Amiram Eldar, Jul 13 2022 *)
PROG
(PARI) a(n)=my(k=1); forprime(p=2, , if(n*eulerphi(k)<k, return(eulerphi(k)), k*=p)
(CoCoA) // CoCoA 5
define a(n) k := 1; p := 1; while k <= n*EulerTotient(k) do p := NextPrime(p); k := k*p; endwhile; return EulerTotient(k); enddefine;
CROSSREFS
KEYWORD
nonn
AUTHOR
Nico Mexis, Jul 13 2022
STATUS
approved