OFFSET
1,1
COMMENTS
Every number of the sequence has at least three different prime factors. Also, the sequence is infinite (it contains all numbers of the form 3^a*5^b*7^c with a,b,c>0). - Emmanuel Vantieghem, Nov 21 2016
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
n = 315 = 3*3*5*7 is not a power of a prime, has 3 prime factors and (3+5)/2=7 divides n.
MAPLE
filter:= proc(n) local F;
F:= numtheory:-factorset(n);
nops(F) > 2 and n mod (min(F)+max(F))/2 = 0
end proc:
select(filter, [seq(i, i=1..10^4, 2)]); # Robert Israel, Nov 21 2016
MATHEMATICA
Rest@ Select[Range@ 6600, Function[n, And[IntegerQ@ #, Divisible[n, #], ! PrimePowerQ@ n] &[(#[[-1, 1]] + #[[1, 1]])/2] &@ FactorInteger@ n]] (* Michael De Vlieger, Nov 24 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Nov 20 2003
STATUS
approved