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A180442 Numbers n such that a sum of two or more consecutive squares beginning with n^2 is a square. 10
1, 3, 7, 9, 11, 13, 15, 17, 18, 20, 21, 22, 25, 27, 28, 30, 32, 38, 44, 50, 52, 55, 58, 60, 64, 65, 67, 73, 74, 76, 83, 87, 91, 103, 104, 106, 112, 115, 117, 119, 121, 124, 128, 129, 131, 132, 137, 140, 142, 146, 158, 168, 170, 172, 175, 178, 181, 183, 192, 193, 197, 199, 200, 204 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

That is, numbers n such that Sum_{i=n..k} i^2 is a square for some k > n.

The paper by Bremner, Stroeker, and Tzanakis describes how they found all n <= 100 by solving elliptic curves. Their solutions are the same as the terms in this sequence. They also show that there are only a finite number of sums of squares beginning with n^2 that sum to a square. For example, starting with 3^2, there are only 3 ways to sum consecutive squares to produce a square: 3^2 + 4^2, 3^2 + ... + 580^2, and 3^2 + ... + 963^2. See A184762, A184763, A184885, and A184886 for more results from their paper.

This sequence is more difficult than A001032, which has the possible lengths of the sequences of consecutive squares that sum to a square. Be careful adding terms to this sequence; a simple search may miss some terms. An elliptic curve needs to be solved for each number.

It is conjectured that the sequence continues 103, 104, 106, 112, 115, 117, 119, 121, 124, 128, 129, 131, 132, 137, 140, 142, 146, 158, 168, 170, 172, 175, 178, 181, 183, 192, 193, 197, 199, 200. - Jean-François Alcover, Sep 17 2013. Conjecture confirmed (see the Schoenfield link below). - Jon E. Schoenfield, Nov 22 2013

LINKS

Jon E. Schoenfield, Table of n, a(n) for n = 1..123 (includes a derivation of the elliptic curves and Magma code used to find the terms)

A. Bremner, R. J. Stroeker, and N. Tzanakis, On Sums of Consecutive Squares, J. Number Theory 62 (1997), 39-70.

K. S. Brown, Sum of Consecutive Nth Powers Equals an Nth Power

Masoto Kuwata, Jaap Top, An elliptic surface related to sums of consecutive squares, Exposition. Math. 12 (1994) 181-192

FORMULA

Numbers n such that A075404(n) > 0.

EXAMPLE

30 is in the sequence because 30^2 + 31^2 + 32^2 + ... + 197^2 + 198^2 = 1612^2.

MATHEMATICA

jmax[11] = jmax[74] = 10^5; jmax[n_ /; n > 91] = 10^6; jmax[_] = 10^4; Reap[For[n = 1, n <= 200, n++, s = n^2; For[j = n+1, j <= jmax[n], j++, s += j^2; If[IntegerQ[Sqrt[s]], Sow[n]; Print[n, "(", j, ", ", Sqrt[s], ")"]; Break[]]]]][[2, 1]] (* Jean-François Alcover, Sep 17 2013, translated and adapted from Pari *)

PROG

(PARI)for(n=1, 100, s=n^2; for(j=n+1, 999999, s+=j^2; if(issquare(s), print1(n, "(", j, ", ", sqrtint(s), ")"); break())))

CROSSREFS

Cf. A180259, A180273, A180274, A180465.

Cf. A075404, A075405, A075406.

Sequence in context: A179197 A097270 A109802 * A165631 A245586 A005818

Adjacent sequences:  A180439 A180440 A180441 * A180443 A180444 A180445

KEYWORD

nonn,nice

AUTHOR

Zhining Yang, Jan 19 2011

EXTENSIONS

Example simplified by Jon E. Schoenfield, Sep 18 2013

More terms from Jon E. Schoenfield, Nov 22 2013

STATUS

approved

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Last modified September 27 13:13 EDT 2020. Contains 337380 sequences. (Running on oeis4.)