A276281 - OEIS

%I #16 Sep 23 2016 02:44:57

%S 1,2,4,5,10,15,25,30,52,75,104,203,225,260,406,780,877,1015,1754,2704,

%T 3045,4140,4385,8280,10556,13155,20700,21147,41209,42294,45604,62100,

%U 105735,115975,178031,215280,231950,317205,579875,678570,769129,840420,1099644

%N Numbers of the form Bell(i)*Bell(j).

%H Vincenzo Librandi, <a href="/A276281/b276281.txt">Table of n, a(n) for n = 1..200</a>

%t Take[Union@Flatten@Table[BellB[i] BellB[j], {i, 0, 60}, {j, i}], 60]

%o (Perl) use ntheory ":all"; my($l,$i,%BP)=(50,0); my @Bell = map { my $n=$_; vecsum(map { stirling($n,$_,2) } 0..$n); } 0..$l;  for my $i (0..$l) { for my $j ($i..$l) { $BP{vecprod($Bell[$i],$Bell[$j])}++ } }  say $i++," $_" for sort {$a<=>$b} keys %BP;  # _Dana Jacobsen_, Sep 07 2016

%Y Cf. A000110, A049997, A272909.

%K nonn,easy

%O 1,2

%A _Vincenzo Librandi_, Sep 04 2016