cp's OEIS Frontend

A261915 Smallest x such that n can be written as n = x^2 + y^2 + z^2 with x >= y >= z >= 0, or -1 if no such x exists.

%I A261915 #30 Jan 23 2018 04:55:47
%S A261915 0,1,1,1,2,2,2,-1,2,2,3,3,2,3,3,-1,4,3,3,3,4,4,3,-1,4,4,4,3,-1,4,5,-1,
%T A261915 4,4,4,5,4,6,5,-1,6,4,5,5,6,5,6,-1,4,6,5,5,6,6,5,-1,6,5,7,5,-1,6,6,-1,
%U A261915 8,6,5,7,6,7,6,-1,6,6,7,5,6,6,7,-1,8,6,8
%N A261915 Smallest x such that n can be written as n = x^2 + y^2 + z^2 with x >= y >= z >= 0, or -1 if no such x exists.
%C A261915 a(n) = -1 iff n is in A004215, a(n) >= 0 iff n is in A000378.
%C A261915 If we maximize x we get A261904.
%H A261915 David Consiglio, Jr., <a href="/A261915/b261915.txt">Table of n, a(n) for n = 0..10000</a>
%H A261915 David Consiglio, Jr., <a href="/A261915/a261915.txt">Python Program</a>
%H A261915 <a href="/index/Su#ssq">Index entries for sequences related to sums of squares</a>
%e A261915 Table showing initial values of n,x,y,z:
%e A261915    0  0  0  0
%e A261915    1  1  0  0
%e A261915    2  1  1  0
%e A261915    3  1  1  1
%e A261915    4  2  0  0
%e A261915    5  2  1  0
%e A261915    6  2  1  1
%e A261915    7 -1 -1 -1
%e A261915    8  2  2  0
%e A261915    9  2  2  1
%e A261915   10  3  1  0
%e A261915   11  3  1  1
%e A261915   12  2  2  2
%e A261915   13  3  2  0
%e A261915   14  3  2  1
%e A261915   15 -1 -1 -1
%e A261915   16  4  0  0
%e A261915   17  3  2  2
%e A261915   18  3  3  0
%e A261915   19  3  3  1
%e A261915   20  4  2  0
%e A261915   ...
%Y A261915 Cf. A000378, A004215, A005875, A261904.
%Y A261915 Analogs for 4 squares: A178786 and A122921.
%K A261915 sign
%O A261915 0,5
%A A261915 _N. J. A. Sloane_, Sep 11 2015
%E A261915 a(17) corrected, more terms from _David Consiglio, Jr._, Sep 11 2015