A030668 Smallest nontrivial extension of n which is a cube.

125, 27, 343, 4096, 512, 64, 729, 8000, 9261, 1000, 110592, 125, 1331, 140608, 15625, 166375, 1728, 185193, 19683, 205379, 216, 226981, 238328, 24389, 250047, 262144, 2744, 287496, 29791, 300763, 314432, 32768, 3375, 343, 35937

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A030669.

Programs

Python

from gmpy2 import iroot
def A030668(n):
    d, nd = 10, 10*n
    while True:
        x = (iroot(nd-1,3)[0]+1)**3
        if x < nd+d:
            return int(x)
        d *= 10
        nd *= 10 # Chai Wah Wu, May 24 2016