A128269 - OEIS

A128269

a(1)=1; a(n) = lcm((number of earlier terms which are coprime to n), (sum of the earlier terms which are coprime to n)).

1, 1, 2, 2, 12, 2, 60, 2, 30, 2, 570, 2, 4116, 2, 144, 2, 39600, 2, 747694, 2, 9720308, 2, 115638138, 2, 1261104380, 2, 3814717230, 2, 137331022698, 2, 2137994925180, 2, 8901006912, 2, 274682981784, 2, 46154014360092, 2, 29022598622, 2

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OFFSET

1,3

COMMENTS

For n > 2, a(n) is even since by induction the sum of coprimes is 1+1+some even numbers. Therefore a(n) = 2 for even n > 2 since only the 1's are coprime.

LINKS

H. v. Eitzen, Table of n, a(n) for n = 1..1000

EXAMPLE

Among {a(1),a(2),...a(8)} the terms which are coprime to 9 are a(1)=a(2)=1 and a(3)=a(4)=a(6)=a(8)=2. There are 6 such terms. And the sum of these terms is 10. So a(8) = lcm(6,10) = 30.

CROSSREFS

Cf. A128268.

Sequence in context: A293231 A286152 A243306 * A109813 A241519 A353767

Adjacent sequences: A128266 A128267 A128268 * A128270 A128271 A128272

KEYWORD

nonn

AUTHOR

Leroy Quet, Feb 22 2007

EXTENSIONS

More terms copied from b-file by Hagen von Eitzen, Jun 24 2009

STATUS

approved