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 A151925 Write n as a sum of positive squares a^2+b^2+c^2+... with gcd(a,b,...) = 1; a(n) = minimal number of squares needed. 3
 1, 2, 3, 4, 2, 3, 4, 5, 3, 2, 3, 4, 2, 3, 4, 5, 2, 3, 3, 4, 3, 3, 4, 5, 2, 2, 3, 4, 2, 3, 4, 5, 3, 2, 3, 4, 2, 3, 4, 5, 2, 3, 3, 4, 3, 3, 4, 5, 3, 2, 3, 4, 2, 3, 4, 5, 3, 2, 3, 4, 2, 3, 4, 5, 2, 3, 3, 4, 3, 3, 4, 5, 2, 2, 3, 4, 3, 3, 4, 5, 3, 2, 3, 4, 2, 3, 4, 5, 2, 3, 3, 4, 3, 3, 4, 5, 2, 3, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Similar to A002828, but only now primitive representations are allowed. Of course a(n) >= A002828(n). From Lagrange's theorem, a(n) <= 5 (see also Estermann, Grosswald, Th. 3, p. 176). Furthermore, it appears (and should be easy to prove) that: a(n) = 1 iff n=1 a(n) = 2 iff n in A008784\{1} a(n) = 3 iff n in A151926 a(n) = 4 iff n == 4 or 7 mod 8 a(n) = 5 iff n == 0 mod 8 REFERENCES Estermann, T., On the representations of a number as a sum of squares, Acta Arith., 45 (1937), 93-125. E. Grosswald, Representations of Integers as Sums of Squares. Springer-Verlag, NY, 1985. LINKS N. J. A. Sloane, Table of n, a(n) for n = 1..1000 N. J. A. Sloane, Fortran program EXAMPLE ..... n .. a(n) ..<- Numbers when squared add to n -> ----------------------------------------------------- ......1......1......1 ......2......2......1......1 ......3......3......1......1......1 ......4......4......1......1......1......1 ......5......2......1......2 ......6......3......1......1......2 ......7......4......1......1......1......2 ......8......5......1......1......1......1......2 ......9......3......1......2......2 .....10......2......1......3 .....11......3......1......1......3 .....12......4......1......1......1......3 .....13......2......2......3 .....14......3......1......2......3 .....15......4......1......1......2......3 .....16......5......1......1......1......2......3 .....17......2......1......4 .....18......3......1......1......4 .....19......3......1......3......3 .....20......4......1......1......3......3 CROSSREFS Sequence in context: A262304 A333609 A273149 * A106653 A173524 A049865 Adjacent sequences:  A151922 A151923 A151924 * A151926 A151927 A151928 KEYWORD nonn AUTHOR N. J. A. Sloane and Vinay Vaishampayan, Aug 06 2009, Aug 07 2009 STATUS approved

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Last modified September 23 12:43 EDT 2021. Contains 347617 sequences. (Running on oeis4.)