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A102344 Numbers n such that the Diophantine equation (x+2)^3-x^3=2*n^2 has solutions. 0
2, 7, 97, 1351, 18817, 262087, 3650401, 50843527, 708158977, 9863382151, 137379191137, 1913445293767, 26650854921601, 371198523608647, 5170128475599457, 72010600134783751, 1002978273411373057 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

n^2=3*(2*x+4)^2+16

LINKS

Table of n, a(n) for n=1..17.

FORMULA

a(n+2)=14*a(n+1)-a(n) for n>=2.

G.f.: x(2-21x+x^2)/(1-14x+x^2). a(n)=7*A007655(n+2)-97*A007655(n+1), n>1. [From R. J. Mathar, Sep 11 2008]

a(n)=-2*sqrt(3)*{[7-4*sqrt(3)]^(n-1)-[7+4*sqrt(3)]^(n-1)}+(7/2)*{[7+4*sqrt(3)]^(n-1)+[7 -4*sqrt(3)]^(n-1)}+[C(2*n,n) mod 2], with n>=0 [From Paolo P. Lava, Nov 25 2008]

EXAMPLE

The first examples are 2^3-0^3=2*2^2 ; 5^3-3^3=2*7^2 ; 57^3-55^3=2*97^2 ; 781^3-779^3=2*1351^2 ; 10865^3-10863^3=2*18817^2

MATHEMATICA

a[1]=2; a[2]=7; a[3]=97; a[n_] := a[n] = 14*a[n-1]-a[n-2]; Table[a[n], {n, 1, 17}] (* Jean-François Alcover, Dec 17 2013 *)

CROSSREFS

Sequence in context: A112290 A072059 A240696 * A087589 A002812 A219280

Adjacent sequences:  A102341 A102342 A102343 * A102345 A102346 A102347

KEYWORD

easy,nonn

AUTHOR

Richard Choulet, Sep 08 2008

EXTENSIONS

Extended by R. J. Mathar, Sep 11 2008

STATUS

approved

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Last modified April 21 02:07 EDT 2014. Contains 240824 sequences.