OFFSET
1,1
COMMENTS
Here lambda is Carmichael's lambda function (see A002322).
LINKS
R. D. Carmichael, Note on a new number theory function, Bull. Amer. Math. Soc. 16 (1910), 232-238.
MATHEMATICA
Select[Range[65520], CarmichaelLambda[#] == 12 &] (* Paolo Xausa, Feb 28 2024 *)
PROG
(PARI)
lambda(n) = { \\ A002322
my(f=factor(n), fsz=matsize(f)[1]);
lcm(vector(fsz, k, my(p=f[k, 1], e=f[k, 2]);
if (p != 2, p^(e-1)*(p-1), e > 2, 2^(e-2), 2^(e-1))));
};
invlambda(n) = { \\ A270562
if (n <= 0, return(0), n==1, return(2), n%2, return(0));
my(f=factor(n), fsz=matsize(f)[1], g=1, h=1);
for (k=1, fsz, my(p=f[k, 1], e=1);
while (n % lambda(p^e) == 0, e++); g *= p^(e-1));
fordiv(n, d, if (isprime(d+1) && g % (d+1) != 0, h *= (d+1)));
g *= h; if (lambda(g) != n, 0, g);
};
lambda_level(n) = {
my(N = invlambda(n)); if (!N, return([])); my(s=List());
fordiv(N, d, if (lambda(d) == n, listput(s, d)));
Set(s);
};
lambda_level(12)
CROSSREFS
KEYWORD
nonn,fini,full
AUTHOR
Gheorghe Coserea, Feb 21 2019
STATUS
approved