A088230 a(1)=0; for n>1: a(n)=a(n-1)-n if that number is nonnegative and occurs at most once in the sequence, otherwise a(n)=a(n-1)+n.

0, 1, 3, 0, 4, 9, 3, 10, 2, 11, 1, 12, 24, 11, 25, 10, 26, 9, 27, 8, 28, 7, 29, 6, 30, 5, 31, 4, 32, 61, 31, 62, 30, 63, 29, 64, 28, 65, 27, 66, 26, 67, 25, 68, 24, 69, 23, 70, 22, 71, 21, 72, 20, 73, 19, 74, 18, 75, 17, 76, 16, 77, 15, 78, 14, 79, 13, 80, 12, 81, 151, 80, 8, 81

Offset: 1

Author

Reinhard Zumkeller, Nov 03 2003

Keywords

• nonn

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to Recamán's sequence.

Crossrefs

Cf. A005132, A008344.

Programs

Haskell

a088230 n = a088230_list !! (n-1)
a088230_list = 0 : f [1..] [0] where
   f (x:xs) ys@(y:_)
    | x <= y && (length $ filter (== z) ys) <= 1 = z : f xs (z : ys)
    | otherwise = (x + y) : f xs ((x + y) : ys)  where z = y - x
-- Reinhard Zumkeller, May 08 2012