OFFSET
1,1
COMMENTS
a(n) = 1 for most n. True for all primes and other integers.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = gcd(n+1, cototient(n)) = gcd(n+1, A051953(n)).
EXAMPLE
n = 247 = 13*19, n+1 = 248 = 8*31, phi(247) = 12*18 = 216, cototient(247) = 247-216 = 31, so a(247) = gcd(248,31) = 31.
MATHEMATICA
Table[GCD[n+1, n-EulerPhi[n]], {n, 0, 110}] (* Harvey P. Dale, Dec 24 2012 *)
PROG
(PARI) A058665(n) = gcd(n+1, n-eulerphi(n)); \\ Antti Karttunen, Jul 28 2017
(Python)
from sympy import gcd, totient
def a(n): return gcd(n + 1, n - totient(n))
print([a(n) for n in range(1, 51)]) # Indranil Ghosh, Jul 29 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 28 2000
EXTENSIONS
Offset corrected by Antti Karttunen, Jul 28 2017
STATUS
approved