A078264 Integer part of the geometric mean of the forward and reverse concatenations of 1 to n.

1, 15, 198, 2309, 25895, 284217, 3074048, 32896079, 349188532, 11646890238, 1171148874112, 122278263238675, 12727490844526758, 1320830780128673820, 136722265049041488664, 14120912163801368446154, 1455577353063960520275521, 149780147487160167412789089

Offset: 1

Author

Amarnath Murthy, Nov 24 2002

Keywords

• base
• nonn

Examples

			a(3) = floor(sqrt(123*321)) = floor(sqrt(39483)) = 198.
		

Crossrefs

Cf. A078263.

Programs

PARI

f="1";b="1";for(i=2,40,print1(sqrtint(eval(f)*eval(b)),",");f=concat(f,Str(i));b=concat(Str(i),b)) \\ Lambert Herrgesell (zero815(AT)googlemail.com), Mar 13 2006

Formula

a(n) = floor(A078263(n)^(1/2)).

Extensions

More terms from Lambert Herrgesell (zero815(AT)googlemail.com), Mar 13 2006