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

1,3

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

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

Crossrefs

Cf. A022442 (complement), A001651.

Sequence in context: A137624 A238246 A330998 * A054353 A284555 A031948

Adjacent sequences: A099464 A099465 A099466 * A099468 A099469 A099470

Keyword

easy,nonn

Author

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

Status

approved