A191767 The earliest increasing sequence of nonnegative integers such that if a(j) < a(k) are both in the sequence then a(k) + 2*(a(k) - a(j)) is not.

0, 1, 2, 5, 7, 8, 9, 12, 16, 28, 29, 33, 35, 37, 40, 42, 51, 57, 58, 59, 65, 76, 78, 86, 92, 117, 123, 127, 130, 131, 134, 138, 141, 165, 166, 182, 183, 186, 187, 190, 201, 203, 205, 208, 211, 215, 247, 257, 268, 280, 317, 329, 338, 350, 352, 354, 360, 395

Offset

1,3

Comments

Start an arithmetic progression with any two terms from the sequence; the fourth term of that progression is not allowed to be in the sequence.

Links

Nathaniel Johnston, Table of n, a(n) for n = 1..5000

Example

Because 0 and 1 are in the sequence, 1 + 2*(1 - 0) = 3 is not in the sequence. Because 5 and 9 are in the sequence, 9 + 2*(9 - 5) = 17 is not in the sequence.

Maple

A191767 := proc(n) option remember; local a, k, j; if n <= 2 then n-1 ; else for a from procname(n-1)+1 do atru := true; for j from 1 to n-2 do for k from j+1 to n-1 do if 3*procname(k)-2*procname(j) = a then atru := false; break; end if; end do: if not atru then break; end if; end do: if atru then return a; end if; end do: end if; end proc: # R. J. Mathar, Jun 30 2011

Crossrefs

Cf. A005836.

Sequence in context: A167408 A047388 A284529 * A374592 A050086 A285352

Adjacent sequences: A191764 A191765 A191766 * A191768 A191769 A191770

Keyword

nonn,easy

Author

Paul Weisenhorn, Jun 15 2011

Status

approved