A080704 a(1)=2; for n>1, if n is in the sequence then a(n) is the smallest even integer > a(n-1), otherwise a(n) = a(n-1) + 3.

2, 4, 7, 8, 11, 14, 16, 18, 21, 24, 26, 29, 32, 34, 37, 38, 41, 42, 45, 48, 50, 53, 56, 58, 61, 62, 65, 68, 70, 73, 76, 78, 81, 82, 85, 88, 90, 92, 95, 98, 100, 102, 105, 108, 110, 113, 116, 118, 121, 122, 125, 128, 130, 133, 136, 138, 141, 142, 145, 148

Offset: 1

Author

Benoit Cloitre, Mar 01 2003

Keywords

• nonn
• easy

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Amiram Eldar, Plot of a(n)/n for n = 10000..100000

Crossrefs

Cf. A080705, A064437, A080717.

Programs

Mathematica

a[1] = 2; a[n_] := a[n] = Module[{s = Array[a, n-1]}, a[n-1] + If[MemberQ[s, n], If[OddQ[a[n-1]], 1, 2], 3]]; Array[a, 100] (* Amiram Eldar, May 14 2022 *)

PARI

for(n=2,400,an[n]=if(setsearch(Set(vector(n-1,i,a(i))),n),if(a(n-1)%2,a(n-1)+1,a(n-1)+2),a(n-1)+3))

Formula

It seems that a(n)/n -> 2.4799.... = 62/25 ?