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 A343724 a(n) is the smallest n-digit square with all digits even. 3
 0, 64, 400, 4624, 26244, 228484, 2022084, 20268004, 202208400, 2006860804, 20220840000, 200084446864, 2002004266084, 20000286620224, 200080402620484, 2000028662022400, 20000086482842244, 200002866202240000, 2000008648284224400, 20000246442286866064 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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) LINKS Chai Wah Wu, Table of n, a(n) for n = 1..61 (terms for n = 1..40 from Robert G. Wilson v) MATHEMATICA 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 *) PROG (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 CROSSREFS Cf. A030098, A343725. Sequence in context: A249984 A221598 A017618 * A231841 A184773 A184765 Adjacent sequences:  A343721 A343722 A343723 * A343725 A343726 A343727 KEYWORD nonn,base AUTHOR Jon E. Schoenfield, May 19 2021 STATUS approved

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Last modified December 6 19:17 EST 2021. Contains 349567 sequences. (Running on oeis4.)