OFFSET
1,1
COMMENTS
A378056(p) = 2 for all odd primes p.
6 is the only even term.
The least term that is not a semiprime is a(114) = 29341 = 13 * 37 * 61, and the least term that has more than 3 distinct prime factors is a(4087545) = 1038565321 = 37 * 61 * 421 * 1093.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
s[n_] := Module[{d = Divisors[n]}, GCD[LCM @@ (d + 1), LCM @@ (Rest @ d - 1)]]; s[1] = 1; Select[Range[13000], CompositeQ[#] && s[#] == 2 &]
PROG
(PARI) is(k) = if(isprime(k), 0, my(d = divisors(k)); gcd(lcm(apply(x->x+1, d)), lcm(apply(x -> if(x > 1, x-1, x), d))) == 2);
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Nov 15 2024
STATUS
approved