A309069 Least k such that the rank of the elliptic curve y^2 = x^3 + k^2 is n.
1, 3, 15, 427, 17353
Offset: 0
Programs
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PARI
{a(n) = my(k=1); while(ellanalyticrank(ellinit([0, 0, 0, 0, k^2]))[1]<>n, k++); k}
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{a(n) = my(k=1); while(ellanalyticrank(ellinit([0, 0, 0, 0, k^2]))[1]<>n, k++); k}
{a(n) = ellanalyticrank(ellinit([0, 0, 0, n^2, 0]))[1]}
a(n,startAt=0)=for(k=startAt, oo, my(t=ellrank(ellinit([-k^2, +1]))); if(t[2]n, warning("k=",k," has rank in ",t[1..2]); next); if(t[1] n, error("Cannot determine if a(",n,") is ",k," or larger; rank is in ",t[1..2])); return(k)) \\ Charles R Greathouse IV, Jul 08 2024
\\ See Aranda link.
The curve C[1] = [-1,1^2] has rank one, with generator [1,-1].The rank of C[2] = [-1,2^2] is 2 because it has two generators:PARI> e=ellinit([-1,2^2] );ellgenerators(e) = [[-1, 2], [0, 2]].If k>1, the curve C[k] always has at least two generators: [0,k], [-1,k], then its minimum rank is two.
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