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%I #18 Mar 23 2021 05:39:23
%S 9,0,900,9025,90000,900601,9000000,90003169,900000000,9000127161,
%T 90000000000,900001331856,9000000000000,90000000369889,
%U 900000000000000,9000000036988900,90000000000000000,900000001801523401
%N Smallest n-digit square starting with 9, or 0 if no such number exists.
%F a(n+1) = (floor(sqrt(9*10^n)) + (n mod 2))^2, a(2)=0. - _Sascha Kurz_, Mar 18 2002
%F a(2k+1) = 9 * 10^(2k) for k >= 0. - _Bernard Schott_, Mar 23 2021
%o (PARI) a(n) = if (n==2, 0, (sqrtint(9*10^(n-1)) + (n-1) % 2)^2); \\ _Michel Marcus_, Mar 23 2021
%Y Cf. A000290, A035076 (roots), A045792.
%Y Cf. 2: A067472, 3: A067473, 4: A067474, 5: A067475, 6: A067476, 7: A067477, 8: A067478.
%K base,easy,nonn
%O 1,1
%A _Amarnath Murthy_, Feb 09 2002
%E More terms from _Sascha Kurz_, Mar 18 2002