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A343724
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a(n) is the smallest n-digit square with all digits even.
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3
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0, 64, 400, 4624, 26244, 228484, 2022084, 20268004, 202208400, 2006860804, 20220840000, 200084446864, 2002004266084, 20000286620224, 200080402620484, 2000028662022400, 20000086482842244, 200002866202240000, 2000008648284224400, 20000246442286866064
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OFFSET
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1,2
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COMMENTS
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From Robert G. Wilson v, May 20 2021: (Start)
The square root of any term is == {0, 2, 8} (mod 10).
Other than 1 and 9, there are no squares which contain only odd digits.
(End)
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LINKS
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Chai Wah Wu, Table of n, a(n) for n = 1..61 (terms for n = 1..40 from Robert G. Wilson v)
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MATHEMATICA
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a[n_] := Block[{k = Floor[ Sqrt[10^n/5]]}, If[OddQ@k, k--]; While[ Union[ EvenQ[ IntegerDigits[ k^2]]] != {True}, k += 2]; k^2]; Array[ a, 20] (* Robert G. Wilson v, May 20 2021 *)
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PROG
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(Python 3.8+)
from math import isqrt
def A343724(n):
if n == 1: return 0
m = isqrt(2*10**(i-1))+1
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
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CROSSREFS
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Cf. A030098, A343725.
Sequence in context: A249984 A221598 A017618 * A231841 A184773 A184765
Adjacent sequences: A343721 A343722 A343723 * A343725 A343726 A343727
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KEYWORD
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nonn,base
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AUTHOR
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Jon E. Schoenfield, May 19 2021
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STATUS
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approved
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