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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.)