A343724 -id:A343724 - cp's OEIS frontend

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

Jon E. Schoenfield, May 19 2021

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

Cf. A030098, A343724.

A343726 Squares with exactly one even digit.

Original entry on oeis.org

0, 4, 16, 25, 36, 49, 81, 121, 169, 196, 361, 529, 576, 729, 961, 1156, 1369, 1521, 1936, 3136, 3721, 3969, 5329, 5776, 5929, 7396, 7569, 7921, 15129, 15376, 17161, 17956, 19321, 31329, 35721, 51529, 53361, 57121, 59536, 97969, 111556, 113569, 119716, 131769

Offset: 1

Jon E. Schoenfield, May 19 2021

The even digit is always one of the last two digits.

The only squares with no digits even are the one-digit odd squares 1 and 9.

Jianing Song, Table of n, a(n) for n = 1..10000

Cf. A000290, A030098, A118070, A343724, A343725.

q:= n-> (l-> is(add(i mod 2, i=l)=nops(l)-1))(convert(n, base, 10)):
select(q, [i^2$i=0..400])[];  # Alois P. Heinz, May 22 2021

Select[Range[0, 400]^2, Count[IntegerDigits[#], ?EvenQ] == 1 &] (* _Amiram Eldar, May 21 2021 *)

isA343726(n) = if(issquare(n) && (n!=0), my(d=digits(n)); #d - vecsum(d%2) == 1, n==0) \\ Jianing Song, May 22 2021

def ok(sq): return sum(d in "02468" for d in str(sq)) == 1
def aupto(limit):
  sqs = (i*i for i in range(int(limit**.5)+2) if i*i <= limit)
  return list(filter(ok, sqs))
print(aupto(131769)) # Michael S. Branicky, May 20 2021

Intersection of A000290 and A118070.

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

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A343726 Squares with exactly one even digit.

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