OFFSET
1,1
COMMENTS
Numbers divisible by p+1 for at least three primes p.
Numbers k with A072627(k) >= 3.
Every positive multiple of a term is a term.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(4) = 30 is a term because it is divisible by 2+1=3, 5+1=6 and 29+1=30.
MAPLE
filter:= proc(n) local D;
D:= convert(numtheory:-divisors(n), list);
numboccur(true, map(t -> isprime(t-1), D))>= 3
end proc:
select(filter, [$1..1000]);
MATHEMATICA
okQ[n_] := DivisorSum[n, Boole[PrimeQ[#-1]]&] >= 3;
Select[Range[1000], okQ] (* Jean-François Alcover, May 16 2023 *)
PROG
(PARI) isok(m) = sumdiv(m, d, isprime(d-1)) >= 3; \\ Michel Marcus, Feb 05 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Feb 04 2021
STATUS
approved