A126091 a(1)=1;a(2)=4; for n>2, a(n)=a(n-2)+3 if n is already in the sequence, a(n)=a(n-2)+1 otherwise.

1, 4, 2, 7, 3, 8, 6, 11, 7, 12, 10, 15, 11, 16, 14, 19, 15, 20, 18, 23, 19, 24, 22, 27, 23, 28, 26, 31, 27, 32, 30, 35, 31, 36, 34, 39, 35, 40, 38, 43, 39, 44, 42, 47, 43, 48, 46, 51, 47, 52, 50, 55, 51, 56, 54, 59, 55, 60, 58, 63, 59, 64, 62, 67, 63, 68, 66, 71, 67, 72, 70, 75

Offset: 1

Author

Zak Seidov, Mar 11 2007

Keywords

• nonn

Crossrefs

Cf. A080578, A080455-A080458.

Programs

Mathematica

a={1,4};Do[If[MemberQ[a,n],b=a[[n-2]]+3,b=a[[n-2]]+1];AppendTo[a,b],{n,3,70}];a