A330772 a(n) = 1 for n<1; for n >= 0, a(n+1) = 2*a(n-a(n)).

2, 2, 2, 4, 2, 4, 4, 4, 8, 4, 8, 4, 8, 4, 8, 8, 8, 16, 4, 16, 8, 16, 8, 16, 8, 16, 8, 8, 32, 2, 16, 16, 16, 16, 32, 4, 32, 4, 32, 8, 32, 16, 32, 16, 16, 64, 2, 32, 16, 32, 32, 8, 32, 16, 8, 4, 16, 64, 2, 32, 16, 32, 4, 4, 64, 4, 64, 4, 8, 32, 8, 8, 8, 128

Offset: 1

Author

Rok Cestnik, Dec 30 2019

Keywords

• nonn

Comments

From the current term count back the same number of terms and double it to obtain the next term. Because a(n) can exceed n, negative indexes are also occasionally referenced.

Examples

			a(1) = 2*a(0-a(0)) = 2*a(-1) = 2.
a(2) = 2*a(1-a(1)) = 2*a(-1) = 2.
a(3) = 2*a(2-a(2)) = 2*a(0) = 2.
a(4) = 2*a(3-a(3)) = 2*a(1) = 4.
		

Crossrefs

Cf. A281130, A070867, A004001.

Programs

Python

a = [2]
for n in range(1000):
    if(a[n] > n):
        a.append(2)
    else:
        a.append(2*a[n-a[n]])