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

1,2

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. [From R. J. Mathar, Aug 18 2008]

Links

Table of n, a(n) for n=1..55.

Prog

(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; (Nickerson)

Crossrefs

Cf. A079759, A109896, A109897.

Sequence in context: A189793 A356141 A079760 * A083209 A339858 A080714

Adjacent sequences: A109892 A109893 A109894 * A109896 A109897 A109898

Keyword

nonn

Author

Amarnath Murthy, Jul 13 2005

Extensions

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

Status

approved