A018930 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

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