A055456 a(n) is the smallest number which is not the sum of exactly 1 or of n earlier terms.

1, 3, 2, 13, 4, 5, 6, 7, 8, 9, 10, 11, 12, 183, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71

Offset

1,2

Links

Table of n, a(n) for n=1..72.

Formula

If n-1 > 0 has not already appeared in sequence then a(n) = n-1, otherwise a(n) = n^2 - n + 1.

Example

a(3)=2 because 1 is already in the sequence, 2 has not yet appeared (i.e., is not the sum of 1 earlier term), and the sum of 3 earlier terms is 3, 5 or 7.
a(4)=13 because 1, 2, and 3 have already appeared and the sum of 4 earlier terms could be any integer from 4 through 12.

Crossrefs

Cf. A035334. a(n) is not n-1 iff n-1 is in A024556 or equivalently in A002065.

Sequence in context: A236435 A218566 A125135 * A198303 A093922 A075555

Adjacent sequences: A055453 A055454 A055455 * A055457 A055458 A055459

Keyword

easy,nonn

Author

Henry Bottomley, May 19 2000

Status

approved