A343725 a(n) is the largest n-digit square with all digits even.

4, 64, 484, 8464, 88804, 868624, 8880400, 86862400, 888040000, 8880800644, 88864802404, 888868068804, 8886826042084, 88886806880400, 888686062262244, 8888680688040000, 88868606226224400, 888868068804000000, 8888600480200862404, 88886806880400000000

Offset

1,1

Links

Chai Wah Wu, Table of n, a(n) for n = 1..63

Prog

(Python 3.8+)
from math import isqrt
def A343725(n):
    m = isqrt(8*(10**i-1)//9)
    m -= m % 2
    k = m**2
    s = set('02468')
    while not set(str(k)) <= s:
        m -= 2
        k -= 4*(m+1)
    return k # Chai Wah Wu, May 20 2021

Crossrefs

Cf. A030098, A343724.

Sequence in context: A169801 A103751 A053959 * A195800 A224446 A128782

Adjacent sequences: A343722 A343723 A343724 * A343726 A343727 A343728

Keyword

nonn,base

Author

Jon E. Schoenfield, May 19 2021

Status

approved