A117823 - OEIS

A117823

a(0) = 0, a(1) = 1; for n >= 2, a(n) = a(n-1) + a(n-2) - n if that number is positive and not already in the sequence, otherwise a(n) = a(n-1) + a(n-2) + n.

%I #6 Sep 03 2017 11:27:16

%S 0,1,3,7,6,8,20,21,33,45,68,102,158,247,391,623,998,1604,2584,4169,

%T 6733,10881,17592,28450,46018,74443,120435,194851,315258,510080,

%U 825308,1335357,2160633,3495957,5656556,9152478,14808998,23961439,38770399

%N a(0) = 0, a(1) = 1; for n >= 2, a(n) = a(n-1) + a(n-2) - n if that number is positive and not already in the sequence, otherwise a(n) = a(n-1) + a(n-2) + n.

%p a[0]:=0: a[1]:=1: A:={0,1}: for n from 2 to 42 do if a[n-1]+a[n-2]-n>0 and member(a[n-1]+a[n-2]-n,A)=false then a[n]:=a[n-1]+a[n-2]-n: A:=A union {a[n-1]+a[n-2]-n} else a[n]:=a[n-1]+a[n-2]+n: A:=A union {a[n-1]+a[n-2]+n} fi: od: seq(a[n],n=0..42); # _Emeric Deutsch_, Apr 30 2006

%Y Cf. A005132, A079053, A117821, A117822, A117824.

%K nonn,easy

%O 0,3

%A _N. J. A. Sloane_, Apr 30 2006

%E More terms from _Emeric Deutsch_, Apr 30 2006