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 A161882 Smallest k such that n^2 = a_1^2 + ... + a_k^2 and all a_i are positive integers less than n. 6
 4, 3, 4, 2, 3, 3, 4, 3, 2, 3, 3, 2, 3, 2, 4, 2, 3, 3, 2, 3, 3, 3, 3, 2, 2, 3, 3, 2, 2, 3, 4, 3, 2, 2, 3, 2, 3, 2, 2, 2, 3, 3, 3, 2, 3, 3, 3, 3, 2, 2, 2, 2, 3, 2, 3, 3, 2, 3, 2, 2, 3, 3, 4, 2, 3, 3, 2, 3, 2, 3, 3, 2, 2, 2, 3, 3, 2, 3, 2, 3, 2, 3, 3, 2, 3, 2, 3, 2, 2, 2, 3, 3, 3, 2, 3, 2, 3, 3, 2, 2, 2, 3, 2, 2, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS Related to hypotenuse numbers: A161882(A009003(n))=2 for all n. Jacobi's four-square theorem can be used to show that a(n) <= 4. - Charles R Greathouse IV, Jul 31 2011 LINKS Alois P. Heinz, Table of n, a(n) for n = 2..700 Jean-Charles Meyrignac, Computing minimal equal sums of like powers. Eric Weisstein's World of Mathematics, Diophantine Equation 2nd Powers. FORMULA a(n)=2 iff n is in A009003 (hypotenuse numbers), a(n)=4 iff n is in A000079 (powers of 2), otherwise a(n)=3. - M. F. Hasler, Dec 17 2014 EXAMPLE 2^2 = 1^2 + 1^2 + 1^2 + 1^2, so a(2)=4. 3^2 = 2^2 + 2^2 + 1^2, so a(3)=3. MATHEMATICA f[n_, k_] := Select[PowersRepresentations[n^2, k, 2], AllTrue[#, 0<#

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Last modified April 21 10:04 EDT 2024. Contains 371852 sequences. (Running on oeis4.)