A214371 If a(n) has not yet been defined then set a(n) = least positive integer that has not yet occurred; also if n>1 and a(n+a(n)) has not yet been defined then set a(n+a(n)) = a(n).

1, 2, 3, 2, 4, 3, 5, 6, 4, 7, 8, 5, 4, 6, 9, 10, 7, 11, 8, 6, 12, 13, 14, 9, 15, 10, 8, 16, 11, 17, 18, 19, 12, 20, 13, 10, 14, 21, 22, 15, 23, 24, 25, 16, 12, 10, 17, 13, 18, 26, 19, 27, 28, 20, 15, 10, 12, 29, 21, 16, 22, 30, 31, 23, 32, 24, 18, 25, 12, 19, 33

Offset: 1

Author

Alex Ratushnyak, Jul 14 2012

Keywords

• nonn
• easy

Crossrefs

Cf. A214370.

Cf. A026242, A026338.

Programs

Mathematica

mex[a_]:=Module[{q}, q=1; While[MemberQ[a,q], q++]; q]; a = Table[0,{k, 1, 100}]; For[n=1, n<=100, n++, {If[a[[n]]==0, a[[n]] = mex[a]]; If[n>1, {nan = n+a[[n]]; If[(nan <= Length[a]) && (a[[nan]] == 0), a[[nan]] = a[[n]]]}]; }]; a

Python

SIZE = 300
a = [-8]*SIZE
top=0
for n in range(SIZE):
    if a[n]==-8:       # if a[n] is undefined yet
        top+=1
        a[n]=top
    if 1
				

Formula

a(1)=1, for n>1, a(n) = A214370(n-1)+1.