A276281 Numbers of the form Bell(i)*Bell(j).

1, 2, 4, 5, 10, 15, 25, 30, 52, 75, 104, 203, 225, 260, 406, 780, 877, 1015, 1754, 2704, 3045, 4140, 4385, 8280, 10556, 13155, 20700, 21147, 41209, 42294, 45604, 62100, 105735, 115975, 178031, 215280, 231950, 317205, 579875, 678570, 769129, 840420, 1099644

Offset

1,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..200

Mathematica

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

Prog

(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

Crossrefs

Cf. A000110, A049997, A272909.

Sequence in context: A058299 A191616 A319909 * A059994 A299492 A253198

Adjacent sequences: A276278 A276279 A276280 * A276282 A276283 A276284

Keyword

nonn,easy

Author

Vincenzo Librandi, Sep 04 2016

Status

approved