A018930 a(1)=3; for n>1, a(n) is smallest positive integer such that a(1)^2+...+a(n)^2 = m^2 for some m.

3, 4, 12, 84, 132, 12324, 1836, 105552, 255084, 197580, 10358340, 13775220, 1936434780, 51299286012, 123205977516, 862441842612, 1310543298204, 667510076211780, 207181940072172, 110912831751840, 1698410314006284

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..100

Mathematica

f[n_]:=Module[{a={3}}, Do[AppendTo[a, First[y/. {ToRules[Reduce[{y^2+a.a == x^2, x>0, y>0}, {y, x}, Integers]]}]], {n-1}]; a]; f[21]//Timing (* Jean-François Alcover, Jan 26 2007 *)

Prog

(PARI) print1("3, "); s=9; for(n=1, 30, d=divisors(s); t=d[#d\2]; q=(s\t-t)/2; print1(q, ", "); s+=q^2); \\ Max Alekseyev, Nov 23 2012

Crossrefs

Cf. A018928, A018929, A127689.

Sequence in context: A298115 A122903 A059792 * A127689 A307077 A330068

Adjacent sequences: A018927 A018928 A018929 * A018931 A018932 A018933

Keyword

nonn

Author

Charles Reed (charles.reed(AT)bbs.ewgateway.org)

Extensions

More terms from David W. Wilson.

Status

approved