A074155 Group the natural numbers so that the product of members of a group is a multiple of the sum: (1),(2,3,4,5,6),(7,8,9),(10,11,12),(13,14,15),(16,17,18),(19,20,21),(22,23,24),.... This is the sequence of the ratio of product /sum.

1, 36, 21, 40, 65, 96, 133, 176, 225, 280, 341, 408, 481, 560, 645, 736, 833, 936, 1045, 1160, 1281, 1408, 1541, 1680, 1825, 1976, 2133, 2296, 2465, 2640, 2821, 3008, 3201, 3400, 3605, 3816, 4033, 4256, 4485, 4720, 4961, 5208, 5461, 5720, 5985, 6256, 6533

Offset

1,2

Comments

a(n+1) = (3n+1)(n+1) for n >=2.

Links

Table of n, a(n) for n=1..47.

Formula

For n>2, a(n) = n(3n-2) = A000567(n).

Maple

1, 36, seq((3*n+1)*(n+1), n=2..120);

Mathematica

Join[{1, 36}, Table[(3n+1)(n+1), {n, 2, 50}]] (* Harvey P. Dale, Sep 04 2019 *)

Crossrefs

Sequence in context: A081726 A196044 A196041 * A126958 A070726 A083819

Adjacent sequences: A074152 A074153 A074154 * A074156 A074157 A074158

Keyword

nonn

Author

Amarnath Murthy, Aug 29 2002

Extensions

More terms from Sascha Kurz, Jan 15 2003

Status

approved