A066203 a(1) = 2; a(2) = 1; for n > 2, 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).

2, 1, 3, 6, 10, 5, 11, 4, 12, 21, 31, 20, 8, 21, 7, 22, 38, 55, 37, 18, 38, 17, 39, 16, 40, 15, 41, 14, 42, 13, 43, 74, 106, 73, 107, 72, 36, 73, 35, 74, 34, 75, 33, 76, 32, 77, 123, 170, 122, 171, 121, 70, 122, 69, 123, 68, 124, 67, 9, 68, 128, 189, 127, 64, 128, 63, 129, 62

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 A066202.

Programs

Python

l=[0, 2, 1]
for n in range(3, 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