A129619 a(n) = largest proper divisor of the sum of all positive integers which are <= n and are not included among the first n-1 terms of the sequence.

1, 1, 1, 3, 1, 1, 12, 16, 1, 17, 31, 31, 25, 1, 52, 52, 52, 61, 47, 23, 91, 102, 102, 114, 114, 127, 1, 103, 169, 184, 184, 200, 1, 1, 251, 269, 115, 1, 326, 346, 1, 155, 409, 431, 1, 1, 1, 143, 525, 550, 1, 1, 602, 629, 101, 37, 463, 1, 753, 783, 783, 814, 89, 585, 910, 943

Offset

1,4

Links

Table of n, a(n) for n=1..66.

Example

The positive integers which are <= 8 and do not occur among the first 7 terms of the sequence are 2,4,5,6,7,8. a(8) is the largest proper divisor of the sum of these integers. 2+4+5+6+7+8 = 32. So a(8) is the largest proper divisor of 32, which is 16.

Mathematica

a = {1}; For[n = 2, n < 70, n++, AppendTo[a, Divisors[n*(n + 1)/2 - Plus @@ Select[Union[a, a], # < n + 1 &]][[ -2]]]]; a (* Stefan Steinerberger, Nov 21 2007 *)

Crossrefs

Sequence in context: A128592 A156584 A209424 * A094573 A055154 A338875

Adjacent sequences: A129616 A129617 A129618 * A129620 A129621 A129622

Keyword

nonn

Author

Leroy Quet, May 30 2007

Extensions

More terms from Stefan Steinerberger, Nov 21 2007

Status

approved