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 January 26th, 2018, 03:30 PM #1 Newbie   Joined: Jan 2018 From: DeLand, Florida Posts: 1 Thanks: 0 Fermat Theorem Question In Fermat's Last Theorem ... do the numbers to the left of the equal sign have to be different? I'm looking for close solutions ... and have (after several years)found two systems which (I think) predicts them ... possibly to infinity. For example 4^3 + 4^3 -3 = 5^3 or 64 + 64 - 3 = 125 This is the ONLY equation I can find which is "off by three" AT ANY POWER. But if the first two numbers must be different, even this is not a valid example. Thank you, OldDumbGuy
 January 26th, 2018, 04:03 PM #2 Global Moderator   Joined: Dec 2006 Posts: 19,866 Thanks: 1833 Any power? 4Â² + 6Â² - 3 = 7Â²
 January 26th, 2018, 04:28 PM #3 Senior Member   Joined: May 2016 From: USA Posts: 1,188 Thanks: 489 The numbers may be the same, but $5^3 + 5^3 = 250 \text { and } 6^3 = 216 \implies 6^3 = 5^3 + 5^3 - 34.$ And 3 does not equal 34. So I do not understand what you are saying. In general $a^3 + a^3 - (a^3 - 3a^2 - 3a - 1) = a^3 + 3a^2 + 3a + 1 = (a + 1)^3.$ $\therefore a = 4 \implies 4^3 - 3 * 4^2 - 3 * 4 - 1 = 64 - 48 - 12 - 1 = 3 \implies$ $4^3 + 4^3 - 3 = 5^3$ but that is not a general result.
 January 26th, 2018, 04:50 PM #4 Global Moderator   Joined: Dec 2006 Posts: 19,866 Thanks: 1833 Really close misses aren't very common, but 6Â³ + 8Â³ + 1 = 9Â³.
January 28th, 2018, 12:21 PM   #5
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Quote:
 Originally Posted by skipjack Really close misses aren't very common...
Can you prove that? I'm curious as to how that would be done.

 January 28th, 2018, 02:08 PM #6 Global Moderator   Joined: Dec 2006 Posts: 19,866 Thanks: 1833 I don't know a proof.
 January 28th, 2018, 02:44 PM #7 Senior Member   Joined: Aug 2012 Posts: 2,076 Thanks: 593 $64^3 + 94^3 = 103^3 + 1$ A Google search for "Fermat near misses" turns up many links on the subject for anyone interested. They're not all that rare but I didn't dig into the details of these articles. https://www.google.com/search?q=ferm...hrome&ie=UTF-8 Ramanujan found an infinite family of near-miss cubes related to his studies (decades ahead of his time) of elliptic curves. https://plus.maths.org/content/ramanujan Thanks from greg1313 and Joppy Last edited by Maschke; January 28th, 2018 at 02:50 PM.

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