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a(n) = floor(sqrt{concatenation n,(n-1),...,3,2,1}).
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%I #11 Jul 22 2024 14:36:56

%S 1,4,17,65,233,808,2766,9362,31426,104822,1054033,11005043,114547418,

%T 1188747707,12305003905,127088210000,1310019623181,13480213329659,

%U 138498072735374,1420979139942389,14560878466498901,149036972532711329,1523880579042109897

%N a(n) = floor(sqrt{concatenation n,(n-1),...,3,2,1}).

%C a(n) = floor(sqrt(A000422(n))). - _Stefan Steinerberger_, May 05 2007

%e a(4) = floor(sqrt(4321)) = 65.

%p a:= n-> floor(sqrt(parse(cat((n-i)$i=0..n-1)))):

%p seq(a(n), n=1..30); # _Alois P. Heinz_, Aug 26 2015

%t Table[Floor[Sqrt[FromDigits[Flatten[Table[IntegerDigits[i],{i,n,1,-1}]]]]],{n,1,25}] (* _Stefan Steinerberger_, May 05 2007 *)

%t Table[Floor[Sqrt[FromDigits[Flatten[IntegerDigits/@Range[n,1,-1]]]]],{n,25}] (* _Harvey P. Dale_, Jul 22 2024 *)

%Y Cf. A068995.

%K base,easy,nonn,less

%O 1,2

%A _Amarnath Murthy_, Jun 17 2004

%E More terms from _Stefan Steinerberger_, May 05 2007