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A244151 0-additive sequence: start with a(1) = 2; thereafter, a(n) = smallest number not already in sequence which is not the sum of any previous two terms. 4
2, 3, 4, 8, 9, 14, 15, 20, 21, 26, 27, 32, 33, 38, 39, 44, 45, 50, 51, 56, 57, 62, 63, 68, 69, 74, 75, 80, 81, 86, 87, 92, 93, 98, 99, 104, 105, 110, 111, 116, 117, 122, 123, 128, 129, 134, 135, 140, 141, 146, 147, 152, 153, 158, 159, 164, 165, 170, 171, 176, 177, 182, 183, 188, 189, 194, 195, 200, 201, 206, 207, 212, 213 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

As A033627, but first term is 2.

4 and the numbers in A047243. - Joerg Arndt, Jun 22 2014

LINKS

Table of n, a(n) for n=1..73.

Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

FORMULA

a(2n) = 6(n-1)+2 & a(2n+1) = 6(n-1)+3 for n>1. - Robert G. Wilson v, Jun 23 2014

a(n) = a(n-1)+a(n-2)-a(n-3) for n>6. - Colin Barker, Jun 26 2014

G.f.: x*(x^5+3*x^3-x^2+x+2) / ((x-1)^2*(x+1)). - Colin Barker, Jun 26 2014

MATHEMATICA

f[s_List] := Block[{k = s[[-1]] + 1, ss = Union[Plus @@@ Subsets[s, {2}]]}, While[ MemberQ[ss, k], k++]; Append[s, k]]; Nest[f, {2}, 70] (* Robert G. Wilson v, Jun 23 2014 *)

PROG

(PARI) Vec(x*(x^5+3*x^3-x^2+x+2)/((x-1)^2*(x+1)) + O(x^100)) \\ Colin Barker, Jun 26 2014

CROSSREFS

Cf. A033627.

Sequence in context: A127483 A130804 A022999 * A057844 A281089 A242333

Adjacent sequences:  A244148 A244149 A244150 * A244152 A244153 A244154

KEYWORD

nonn,easy

AUTHOR

Leonardo Sznajder, Jun 21 2014

EXTENSIONS

Added terms >= 20, Joerg Arndt, Jun 22 2014

STATUS

approved

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Last modified October 15 00:04 EDT 2019. Contains 328025 sequences. (Running on oeis4.)