A249055 a(1)=0; the next term is always the product of the two smallest numbers not yet in the sequence and which have not yet been used.

0, 2, 12, 30, 56, 90, 143, 210, 272, 342, 420, 506, 600, 702, 812, 992, 1122, 1260, 1406, 1560, 1722, 1892, 2070, 2256, 2450, 2652, 2862, 3135, 3422, 3660, 3906, 4160, 4422, 4692, 4970, 5256, 5550, 5852, 6162, 6480, 6806, 7140, 7482, 7832, 8372, 8742, 9120, 9506, 9900

Offset

1,2

Comments

Suggested by A075336 and A249406.

Links

Table of n, a(n) for n=1..49.

Example

Start with a(1) = 0. The missing numbers are 1 2 3 4 5 6 ...
Multiply the first two, and we get 2, which is therefore a(2).
Cross 1, 2, and 1*2 = 2 off the missing list.
The first two missing numbers are now 3 and 4, so a(3) = 3*4 = 12.
Cross off 3,4,12 from the missing list.
Repeat!

Maple

M:=50; A:=[0]; miss:=[seq(n, n=1..M^2)]:
for n from 1 to M do t1:=miss[1]*miss[2]; A:=[op(A), t1];
miss:=[seq(miss[i], i=3..nops(miss))];
miss:=remove('x->x=t1', miss);
od:
A;

Crossrefs

Cf. A075326, A000045, A249406, A000304, A000301.

Sequence in context: A067348 A002939 A118239 * A127118 A259127 A296257

Adjacent sequences: A249052 A249053 A249054 * A249056 A249057 A249058

Keyword

nonn

Author

N. J. A. Sloane, Nov 01 2014

Extensions

Typo in definition corrected by Douglas Latimer, Nov 01 2014

Status

approved