Lagrange's Theorem

[Numbers]

After reading this :

http://www.mersenneforum.org/showthr...t=Lucas+Lehmer

particularly the second post, by R. D. Silverman, I was trying to find the Lagrange's Theorem he refers to. But looking on Mathworld there’s about twenty entries for Lagrange and I can’t figure out which one he is referring to. Would anyone mind pointing me in the right direction?

Thanks,

[R.D. Silverman]

Originally Posted by Numbers

After reading this :

http://www.mersenneforum.org/showthr...t=Lucas+Lehmer

particularly the second post, by R. D. Silverman, I was trying to find the Lagrange's Theorem he refers to. But looking on Mathworld there’s about twenty entries for Lagrange and I can’t figure out which one he is referring to. Would anyone mind pointing me in the right direction?

Thanks,

Lagrange's Theorem can be expressed in more than one way.

The usual way is: "The order of an element (in a group) divides the order
of the group"

Equivalently: "The size of a sub-group divides the order of its parent group"

[akruppa]

The particular MathWorld page is http://mathworld.wolfram.com/LagrangesGroupTheorem.html
but the theorem is stated in a very general form there, so that it applies to infinite groups as well. It is more accessible the way Bob stated it.

Alex