A099467 a(1) = a(2) = 1; for n > 2, a(n) is the smallest number > a(n-1) which is not the sum of 2 consecutive elements of the sequence.

1, 1, 3, 5, 6, 7, 9, 10, 12, 14, 15, 17, 18, 20, 21, 23, 24, 25, 27, 28, 30, 31, 33, 34, 36, 37, 39, 40, 42, 43, 45, 46, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 65, 66, 68, 69, 71, 72, 74, 75, 77, 78, 80, 81, 83, 84, 86, 87, 89, 90, 92, 93, 95, 96, 97

Offset: 1

Author

Gaetan Polard (gaetan27(AT)hotmail.com), Nov 18 2004

Keywords

• easy
• nonn

Comments

The first differences are 1 and 2 strictly alternately, except near powers of 2: a(2^k+2)-a(2^k+1) = a(2^k+1)-a(2^k). Cf. A001651 which is generated by the same rule if we start from 1, 2 and has first differences 1, 2, 1, 2... with no exceptions. - Andrey Zabolotskiy, Feb 11 2021

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A022442 (complement), A001651.

Programs

Maple

A[1]:= 1: A[2]:= 1: forbid:= {2}:
for n from 3 to 100 do
  for k from A[n-1]+1 while member(k, forbid) do od:
  A[n]:= k;
  forbid:= forbid union {A[n-1]+k};
od:
seq(A[i],i=1..100); # Robert Israel, Nov 29 2017