OFFSET
1,6
COMMENTS
LCM of common divisors of n and sigma(n). It equals n if n is multiply perfect (A007691). - Labos Elemer, Aug 14 2002
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
P. Pollack, On the greatest common divisor of a number and its sum of divisors, Michigan Math. J. Volume 60, Issue 1 (2011), 199-214.
FORMULA
a(n) = n/A017666(n). - Antti Karttunen, May 22 2017
MATHEMATICA
Table[GCD[n, DivisorSigma[1, n]], {n, 110}] (* Harvey P. Dale, Aug 23 2015 *)
PROG
(Haskell)
a009194 n = gcd (a000203 n) n -- Reinhard Zumkeller, Mar 23 2013
(PARI) a(n) = gcd(n, sigma(n)); \\ Michel Marcus, Oct 23 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved