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

1,2

Links

Table of n, a(n) for n=1..18.

Formula

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

Example

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

Prog

(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

Crossrefs

Cf. A078263.

Sequence in context: A152587 A060337 A180789 * A322914 A014896 A048444

Adjacent sequences: A078261 A078262 A078263 * A078265 A078266 A078267

Keyword

base,nonn

Author

Amarnath Murthy, Nov 24 2002

Extensions

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

Status

approved