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 A034404 Values of C(n,3) which can be written as C(x,3) + C(y,3). 3
 20, 680, 29260, 34220, 70300, 221815, 227920, 287980, 467180, 908600, 2481115, 4278680, 12259940, 13813570, 15493204, 17861900, 19970444, 24672560, 25665020, 27880600, 29742164, 34055980, 44722580 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Bombieri's Napkin Problem: Bombieri said that "the equation C(x,n) + C(y,n) = C(z,n) has no trivial solutions for n >= 3" (the joke being that he said "trivial" rather than "nontrivial"!). Also: tetrahedral numbers that are the sum of two other tetrahedral numbers. (For the indices of these terms, see A002311.) - Harvey P. Dale, Jul 25 2011 REFERENCES Van der Poorten, Notes on Fermat's Last Theorem, Wiley, p. 122. LINKS FORMULA a(n) = A000292(A002311(n)). - Reinhard Zumkeller, May 02 2014 EXAMPLE C(10,3) + C(16,3) = C(17,3) = 680. MATHEMATICA With[{tetras=Binomial[Range[700]+2, 3]}, Union[Select[Total/@Tuples[ tetras, 2], MemberQ[tetras, #]&]]] (* Harvey P. Dale, Jul 25 2011 *) PROG (Haskell) a034404 = a000292 . a002311  -- Reinhard Zumkeller, May 02 2014 CROSSREFS Cf. A010330, A002311. Sequence in context: A006410 A159874 A203136 * A179712 A012802 A049214 Adjacent sequences:  A034401 A034402 A034403 * A034405 A034406 A034407 KEYWORD nonn,nice AUTHOR STATUS approved

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Last modified October 20 01:58 EDT 2020. Contains 337897 sequences. (Running on oeis4.)