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A099426 Numbers n where n^2 = x^3 + y^3; x,y>0 and gcd(x,y)=1. 7
3, 228, 671, 1261, 6371, 9765, 35113, 35928, 40380, 41643, 66599, 112245, 124501, 127499, 167160, 191771, 205485, 255720, 297037, 377567, 532392, 546013, 647569, 681285, 812340, 897623, 1043469, 1125683, 1261491, 1431793, 1433040, 1584828, 1783067, 1984009, 2107391, 2372903, 2440893, 2484469, 2548557 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Based on an observation of Ed Pegg Jr, who supplied terms a(2)-a(6) and a(8).

LINKS

Joerg Arndt and Donovan Johnson, Table of n, a(n) for n = 1..300 (first 55 terms from Joerg Arndt)

EXAMPLE

228 is in the sequence because 228^2 = 11^3 + 37^3 and gcd(11, 37) = 1.

MATHEMATICA

n = 10^7; n2 = n^2; x = 1; x3 = x^3; Reap[ While[x3 < n2, y = x + 1; y3 = y^3; While[y3 < n2, If[GCD[x, y] == 1, s = x3 + y3; If[ IntegerQ[r = Sqrt[s]], Print[r]; Sow[r]; Break[]]]; y += 1; y3 = y^3]; x += 1; x3 = x^3]][[2, 1]] // Sort (* Jean-Fran├žois Alcover, Jan 11 2013, translated from Joerg Arndt's 2nd Pari program *)

PROG

(PARI)

is_A099426(n)=

{

    my(n2=n^2, k=1, k3=1, r);

    while( k3 < n2,

        if ( ispower(n2-k3, 3, &r),

            if ( gcd(r, k)==1, return(1) );

        );

        k+=1;  k3=k^3;

    );

    return(0);

}

for (n=1, 10^8, if( is_A099426(n), print1(n, ", ")) );

/* Joerg Arndt, Sep 30 2012 */

(PARI)

/* compute all terms below a threshold at once, terms need to be sorted */

{ N = 10^7; N2 = N^2;

x=1; x3=x^3;

while ( x3 < N2,

    y=x+1; y3=y^3;

    while ( y3 < N2,

        if ( gcd(x, y) == 1,

            s = x3 + y3;

            if ( issquare(s, &r), print(r); break(); );

        );

        y+=1;  y3 = y^3;

    );

    x+=1;  x3 = x^3;

); }

/* Joerg Arndt, Sep 30 2012 */

(PARI) for(s=2, 1e5, for(x=1, s\2, my(y=s-x); if(gcd(x, y)>1, next); if(issquare(x^3+y^3), print1(s", ")))) \\ Charles R Greathouse IV, Nov 06 2014

CROSSREFS

Cf. A099532, A099533, A103255 (min(x,y), sorted).

Sequence in context: A131493 A228871 A195500 * A332123 A100201 A159807

Adjacent sequences:  A099423 A099424 A099425 * A099427 A099428 A099429

KEYWORD

nonn

AUTHOR

Hans Havermann, Oct 15 2004

EXTENSIONS

More terms from Hans Havermann and Bodo Zinser, Oct 20 2004

STATUS

approved

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Last modified June 12 10:58 EDT 2021. Contains 344947 sequences. (Running on oeis4.)