The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A018930 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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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.
(history; published version)

#29 by N. J. A. Sloane at Fri Oct 11 20:31:53 EDT 2013

STATUS

proposed

approved

#28 by Jon E. Schoenfield at Fri Oct 11 17:28:41 EDT 2013

STATUS

editing

proposed

#27 by Jon E. Schoenfield at Fri Oct 11 17:28:38 EDT 2013

NAME

Define {b(n)} by ba(1)=3, b(; for n) >1, a(n >= 2) is smallest number positive integer such that ba(1)^2+...+ba(n)^2 = m^2 for some m and all b(i) are distinct. Sequence gives values of b(n).

#26 by Michel Marcus at Mon Oct 07 11:27:35 EDT 2013

STATUS

proposed

editing

#25 by Jon E. Schoenfield at Mon Oct 07 11:24:08 EDT 2013

STATUS

editing

proposed

Discussion

Mon Oct 07

11:27

Michel Marcus: Maybe in name replace b(x) by a(x) ?
And remove last sentence ?
Because b(n) is actually a(n), no ?

#24 by Jon E. Schoenfield at Mon Oct 07 11:24:06 EDT 2013

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 *)

CROSSREFS

Cf. A018928, A018929, A127689.

AUTHOR

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

STATUS

approved

editing

#23 by OEIS Server at Sun Jul 28 17:47:36 EDT 2013

LINKS

Vincenzo Librandi, <a href="/A018930/b018930_2.txt">Table of n, a(n) for n = 1..100</a>

#22 by Bruno Berselli at Sun Jul 28 17:47:35 EDT 2013

STATUS

proposed

approved

Discussion

Sun Jul 28

17:47

OEIS Server: Installed new b-file as b018930.txt.  Old b-file is now b018930_2.txt.

#21 by Vincenzo Librandi at Sun Jul 28 13:04:10 EDT 2013

STATUS

editing

proposed

#20 by Vincenzo Librandi at Sun Jul 28 13:03:58 EDT 2013

LINKS

Vincenzo Librandi, <a href="/A018930/b018930_1.txt">Table of n, a(n) for n = 1..70</a>