OFFSET
1,1
COMMENTS
Conjecture: This consists exactly of the semiprimes p*q for which p + q divides p*q + 1. - Mohamed Bouhamida, Aug 17 2009 (Comment edited by N. J. A. Sloane, Sep 01 2019.)
LINKS
Robert Israel, Table of n, a(n) for n = 1..2100
MAPLE
filter:= proc(n) local k, D, j, t;
D:= select(t -> t^2 <= n, numtheory:-divisors(n));
j:= max(D);
t:= j+n/j;
andmap(k -> (k+n/k) mod t = 0, D);
end proc:
count:= 0: S:= NULL:
for n from 2 while count < 100 do
if isprime(n) then next
elif filter(n) then
count:= count+1;
S:= S, n;
fi
od:
S; # Robert Israel, Sep 01 2019
MATHEMATICA
Select[Reap[Module[{n, k}, For[n = 1, n < 10000, n++, k = Max[Select[Divisors[n], # <= Sqrt[n]&]]; If[Length[Union[ Mod[Divisors[n] + n/Divisors[n], k+n/k]]] == 1, Sow[n]]]]][[2, 1]], CompositeQ] (* Jean-François Alcover, Feb 07 2023 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Aug 24 2008
EXTENSIONS
More terms from M. F. Hasler, Aug 25 2008
a(33)-a(46) from Ray Chandler, Jun 21 2009
STATUS
approved