OFFSET
1,1
COMMENTS
It suffices to check all bases 2 <= b <= (n+1)/2.
Squarefree composite numbers n such that for every prime p dividing n, p-1 divides gpf(n)-1. - Robert Israel, Sep 18 2016
An even number 2m is in the sequence iff m is an odd prime or odd m is in the sequence. - Altug Alkan and Thomas Ordowski, Sep 19 2016
Problem: are there infinitely many Carmichael numbers A002997 in the sequence? These are Carmichael numbers m such that m/gpf(m) is a Carmichael number, they are a proper subset of A214758. - Thomas Ordowski and Altug Alkan, Sep 19 2016
Squarefree composite numbers n such that A002322(n) = gpf(n)-1. - Thomas Ordowski, Feb 25 2018
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
filter:= proc(n) local F, p;
if isprime(n) or not numtheory:-issqrfree(n) then return false fi;
F:= numtheory:-factorset(n);
p:= max(F);
evalb(map(t -> (p-1) mod (t-1), F) = {0})
end proc:
select(filter, [$2..1000]); # Robert Israel, Sep 18 2016
MATHEMATICA
Select[DeleteCases[Range@ 200, k_ /; ! CompositeQ@ k], Function[n, Times @@ Boole@ Map[Mod[#, n] == Mod[#^(FactorInteger[n][[-1, 1]]), n] &, Range[2, Floor[(n + 1)/2]]] == 1]] (* Michael De Vlieger, Sep 19 2016 *)
PROG
(PARI) is(n)=if(n%2==0, if(n%4, if(isprime(n/2), return(1), n>>=1), return(0))); my(f=factor(n)); if(#f~ < 2 || vecmax(f[, 2])>1, return(0)); for(i=1, #f~, if((f[#f~, 1]-1)%(f[i, 1]-1), return(0))); 1 \\ Charles R Greathouse IV, Sep 19 2016
(PARI) lista(nn) = forcomposite(n=1, nn, if ( issquarefree(n) && !((vecmax(factor(n)[, 1]) - 1) % lcm(znstar(n)[2])), print1(n, ", "))); \\ Michel Marcus, Sep 11 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Ordowski, Sep 18 2016
EXTENSIONS
More terms from Michel Marcus and Robert Israel, Sep 18 2016
STATUS
approved