A333548 Numbers k such that A005132(k-1) = k.

3, 11, 39, 248, 844, 2752, 57071, 58056875

Offset: 1

Author

N. J. A. Sloane, May 01 2020

Keywords

• nonn
• more

Comments

Subtracting 1 from k gives the index of a term A005132(k-1) = k in Recamán's sequence A005132 such that subtracting k would reach 0. This is not permitted, so we must add k instead, obtaining A005132(k) = 2*k.

If A005132(k-1) = k, A005132(k) = 2*k. The converse is not always true. For example, A005132(75) = 228 and A005132(76) = 228 - 76 = 152. - Seiichi Manyama, May 02 2020

Examples

			A005132(10)=11, so 11 is a term (and A005132(11)=22).
		

Links

• Index entries for sequences related to Recamán's sequence

Crossrefs

Cf. A005132, A064568, A064569, A187921, A187922, A331659.

Programs

Python

A333548_list, A005132_set, y = [], {0}, 0
for n in range(1,10**10):
    y -= n
    if y <= 0 or y in A005132_set:
        y += 2*n
    A005132_set.add(y)
    if y == n+1:
        A333548_list.append(y) # Chai Wah Wu, May 02 2020

Extensions

a(8) from Chai Wah Wu, May 02 2020