A030690 Smallest nontrivial extension of n-th square which is a cube.

125, 4096, 9261, 166375, 250047, 3652264, 4913, 64000, 8120601, 1000, 12167, 1442897, 16974593, 19683, 225866529, 25672375, 28934443, 3241792, 3616805375, 40001688, 4410944, 4843965888, 529475129, 5764224257

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Links

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

Crossrefs

Cf. A030691.

Programs

Python

from gmpy2 import iroot
def A030690(n):
    d, nd = 10, 10*n**2
    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