A109895 Group the natural numbers so that every 2n-th group product is divisible by the single number in the next group. (1), (2,3,4,5), (6), (7,8,9,10,11), (12), (13,14,15,16,17,18,19),(20), (21,22,23,24,25,26,27),(28),... Sequence contains the single members of the odd numbered groups.

1, 6, 12, 20, 28, 36, 45, 56, 70, 80, 90, 104, 112, 120, 132, 140, 154, 168, 180, 192, 208, 220, 234, 250, 264, 280, 297, 312, 324, 336, 350, 360, 378, 396, 416, 432, 448, 462, 480, 495, 504, 520, 539, 560, 576, 594, 612, 630, 640, 660, 672, 693, 714, 728, 748

Offset: 1

Author

Amarnath Murthy, Jul 13 2005

Keywords

• nonn

Comments

a(n) divides (a(n)-1)! / (a(n-1)!) and is the smallest integer with this property. - Simon Nickerson (simonn(AT)maths.bham.ac.uk), Jul 15 2005

Essentially a duplicate of A079760. - R. J. Mathar, Aug 18 2008

Crossrefs

Cf. A079759, A109896, A109897.

Programs

GAP

A := [ 1 ]; n := 1; repeat p := 1; k := n + 1; repeat p := p * k; k := k+1; until p mod k = 0; n := k; Add(A, n); until n > 10000; # Simon Nickerson

Extensions

More terms from Simon Nickerson (simonn(AT)maths.bham.ac.uk), Jul 15 2005