OFFSET
1,1
COMMENTS
All numbers not equal to some 2^k or 5*2^k [Fraser and Gordon]. - Joseph Biberstine (jrbibers(AT)indiana.edu), Jul 28 2006
REFERENCES
T. Nagell, Introduction to Number Theory, Wiley, 1951, p. 194.
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
O. Fraser and B. Gordon, On representing a square as the sum of three squares, Amer. Math. Monthly, 76 (1969), 922-923.
FORMULA
a(n) = n + 2*log_2(n) + O(1). - Charles R Greathouse IV, Sep 01 2015
A169580(n) = a(n)^2. - R. J. Mathar, Aug 15 2023
MATHEMATICA
z=100; lst={}; Do[a2=a^2; Do[b2=b^2; Do[c2=c^2; e2=a2+b2+c2; e=Sqrt[e2]; If[IntegerQ[e]&&e<=z, AppendTo[lst, e]], {c, b, 1, -1}], {b, a, 1, -1}], {a, 1, z}]; Union@lst (* Vladimir Joseph Stephan Orlovsky, May 19 2010 *)
PROG
(PARI) is(n)=if(n%5, n, n/5)==2^valuation(n, 2) \\ Charles R Greathouse IV, Mar 12 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Ralph Peterson (ralphp(AT)library.nrl.navy.mil)
EXTENSIONS
More terms from T. D. Noe, Mar 04 2010
STATUS
approved