The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A127689 a(1)=3; for n>1, a(n) is least number such that a(n) > a(n-1) and a(1)^2+...+a(n)^2 is a square. 3
 3, 4, 12, 84, 132, 12324, 15960, 26280, 27300, 66660, 115188, 9777193284, 23465263884, 48701491080, 40900397690640, 680008604512020, 127049882801497788, 247290967245178188, 335580091290976716, 1045885075937364972, 1607091702050097396, 3419793695168900508, 5138020847719969956, 10059508412964112740 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Without the a(n) > a(n-1) constraint, the sequence would be A018930. LINKS EXAMPLE a(2)=4 because 3^2+4^2=5^2, a(3)=12 because 3^2+4^2+12^2=13^2 etc. MATHEMATICA a = {3}; For[k = 1 + a[[Length[a]]], Length[a] < 11, While[ ! IntegerQ[Sqrt[(k)^2 + Sum[(a[[t]])^2, {t, 1, Length[a]}]]], k++ ]; AppendTo[a, k]]; a PROG (PARI) q=3; s=9; for(n=1, 30, b=0; fordiv(s, d, if(d*d>=s, break); t=(s\d-d)/2; if(t>q, b=t); ); q=b; print1(q, ", "); s+=q^2); \\ Max Alekseyev, Nov 23 2012 CROSSREFS Cf. A018930, A127690, A127691. Sequence in context: A122903 A059792 A018930 * A307077 A330068 A127690 Adjacent sequences: A127686 A127687 A127688 * A127690 A127691 A127692 KEYWORD nonn AUTHOR Artur Jasinski, Jan 23 2007 EXTENSIONS More terms from Max Alekseyev, Nov 23 2012 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified November 27 06:50 EST 2022. Contains 358362 sequences. (Running on oeis4.)