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.

0, 1, 3, 7, 6, 8, 20, 21, 33, 45, 68, 102, 158, 247, 391, 623, 998, 1604, 2584, 4169, 6733, 10881, 17592, 28450, 46018, 74443, 120435, 194851, 315258, 510080, 825308, 1335357, 2160633, 3495957, 5656556, 9152478, 14808998, 23961439, 38770399

Offset

0,3

Links

Table of n, a(n) for n=0..38.

Maple

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

Crossrefs

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

Sequence in context: A296343 A347155 A371240 * A338067 A178242 A352168

Adjacent sequences: A117820 A117821 A117822 * A117824 A117825 A117826

Keyword

nonn,easy

Author

N. J. A. Sloane, Apr 30 2006

Extensions

More terms from Emeric Deutsch, Apr 30 2006

Status

approved