OFFSET
1,2
COMMENTS
Conjecture: If n is Carmichael then a(n) = n.
Are the fixed points of this sequence the numbers satisfying Korselt's criterion?
LINKS
Peter Luschny, Table of n, a(n) for n = 1..10000
FORMULA
a(prime(n)) = prime(n).
a(n) = n^2/gcd(n*N(n-1), D(n-1)), with N(k)/D(k) = B(k) the k-th Bernoulli number.
MAPLE
MATHEMATICA
a[n_] := Module[{b = BernoulliB[n - 1]}, n^2 * Denominator[n * b] / Denominator[b]]; Array[a, 60] (* Amiram Eldar, Apr 26 2024 *)
PROG
(PARI) a(n) = n^2*denominator(n*bernfrac(n-1))/denominator(bernfrac(n-1)); \\ Michel Marcus, Jul 17 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Luschny, Jul 16 2019
STATUS
approved