OFFSET
1,1
COMMENTS
Composite numbers k such that lambda(k) divides k-1 and lambda(k-1) divides k-1, where lambda(m) = A002322(m).
These are composites k such that b^(k-1) == 1 (mod (k-1)*k) for every b coprime to (k-1)*k.
Composites k such that B^(b^(k-1)-1) == 1 (mod k^2) for every B coprime to k and for every b coprime to (k-1)*k.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[1, 10^6, 2], CompositeQ[#] && And @@ Divisible[# - 1, CarmichaelLambda[# + {-1, 0}]] &] (* Amiram Eldar, Aug 12 2024 *)
PROG
(PARI) f(n) = lcm(znstar(n)[2]); \\ A002322
isok(k) = !isprime(k) && !((k-1) % f(k)) && !((k-1) % f(k-1)); \\ Michel Marcus, Aug 13 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Ordowski, Aug 12 2024
EXTENSIONS
More terms from Amiram Eldar, Aug 12 2024
STATUS
approved