A066199 a(1) = 1; for n > 1, a(n) = a(n-1)-(n+1) if this is positive and has not already appeared in the sequence, otherwise a(n) = a(n-1)+(n+1).

1, 4, 8, 3, 9, 2, 10, 19, 29, 18, 6, 19, 5, 20, 36, 53, 35, 16, 36, 15, 37, 14, 38, 13, 39, 12, 40, 11, 41, 72, 104, 71, 105, 70, 34, 71, 33, 72, 32, 73, 31, 74, 30, 75, 121, 168, 120, 169, 119, 68, 120, 67, 121, 66, 122, 65, 7, 66, 126, 187, 125, 62, 126, 61, 127, 60, 128

Offset: 1

Author

N. J. A. Sloane, Dec 16 2001

Keywords

• nonn
• easy

Links

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

Crossrefs

A variant of A005132. A row of the array in A066201.

Programs

Python

l=[0, 1]
for n in range(2, 101):
    x=l[n - 1] - (n + 1)
    if x>0 and x not in l: l.append(x)
    else: l.append(l[n - 1] + (n + 1))
print(l[1:]) # Indranil Ghosh, Jun 02 2017

Extensions

More terms from Sascha Kurz, Mar 24 2002