OFFSET
1,1
COMMENTS
If n is a Carmichael number with n-1 squarefree, then n is in the sequence. The smallest such n = 139952671.
If (n-1)/lambda(n) is a prime (see A174590), then n is in the sequence. - Thomas Ordowski, Oct 17 2016
Numbers n such that gcd(phi(n),n-1) = lambda(n)^2 are 1, 2, 2320690177, ? - Thomas Ordowski and Michel Marcus, Oct 20 2016
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[ Range@ 6100000, CompositeQ@# && GCD[ EulerPhi@#, # - 1] == CarmichaelLambda@# &] (* Michael De Vlieger, Nov 01 2015 *)
PROG
(PARI) forcomposite(n=1, 1e7, if(gcd(eulerphi(n), n-1)==lcm(znstar(n)[2]), print1(n ", "))) \\ Altug Alkan, Nov 01 2015
(PARI) t(n)=my(f=factor(n)); for(i=1, #f[, 1], if(f[i, 2]>1||(n-1)%(f[i, 1]-1), return(0))); 1;
is(n)=n%2 && !isprime(n) && t(n) && n>1;
c(n)=gcd(eulerphi(n), n-1)/lcm(znstar(n)[2]);
for(n=1, 1e7, if(is(n) && c(n)==1 , print1(n", "))) \\ Altug Alkan, Nov 01 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Ordowski, Nov 01 2015
EXTENSIONS
More terms from Altug Alkan, Nov 01 2015
STATUS
approved