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A053964
Numbers k such that k^2 contains only digits {4,7,9}.
1
2, 3, 7, 88, 212, 893, 69242288, 8819171038, 865996535661545126193725357
OFFSET
1,1
FORMULA
a(n) = sqrt(A053965(n)).
PROG
(Python)
from itertools import product
from sympy import integer_nthroot
A053964_list = []
for l in range(1, 21):
for p in product(*['479']*l):
a, b = integer_nthroot(int(''.join(p)), 2)
if b:
A053964_list.append(a) # Chai Wah Wu, Apr 01 2021
CROSSREFS
Cf. A053965.
Sequence in context: A065002 A288800 A247025 * A308730 A062578 A062529
KEYWORD
nonn,base,more
AUTHOR
Patrick De Geest, Mar 15 2000
EXTENSIONS
More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Jan 03 2005
a(9) from Zhao Hui Du, Feb 29 2024
STATUS
approved