

A001235


Taxicab numbers: sums of 2 cubes in more than 1 way.


47



1729, 4104, 13832, 20683, 32832, 39312, 40033, 46683, 64232, 65728, 110656, 110808, 134379, 149389, 165464, 171288, 195841, 216027, 216125, 262656, 314496, 320264, 327763, 373464, 402597, 439101, 443889, 513000, 513856, 515375, 525824, 558441, 593047, 684019, 704977
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OFFSET

1,1


COMMENTS

From Wikipedia: "1729 is known as the HardyRamanujan number after a famous anecdote of the British mathematician G. H. Hardy regarding a hospital visit to the Indian mathematician Srinivasa Ramanujan. In Hardy's words: 'I remember once going to see him when he was ill at Putney. I had ridden in taxi cab number 1729 and remarked that the number seemed to me rather a dull one, and that I hoped it was not an unfavorable omen. "No," he replied, "it is a very interesting number; it is the smallest number expressible as the sum of two cubes in two different ways."'"
A011541 gives another version of "taxicab numbers".


REFERENCES

R. K. Guy, Unsolved Problems in Number Theory, Section D1.
G. H. Hardy, Ramanujan, Cambridge Univ. Press, 1940, p. 12.
Ya. I. Perelman, Algebra can be fun, pp. 142143.
H. W. Richmond, On integers which satisfy ..., Trans. Camb. Phil. Soc., 22 (1920), 389403, see p. 402.
D. Wells, The Penguin Dictionary of Curious and Interesting Numbers. Penguin Books, NY, 1986, 165.


LINKS

T. D. Noe and Moshe Levin, Table of n, a(n) for n = 1..10000 (terms a(1)a(4724) from T. D. Noe).
J. CharlesÉ, Recreomath, Ramanujan's Number
A. Grinstein, Ramanujan and 1729
Istambul Bilgi University, Ramanujan and Hardy's Taxi
Christopher Lane, The First ten Ta(2) and their double distinct cubic sums representations, Find Ramanujan's Taxi Number using JavaScript
J. Leech, Some solutions of Diophantine equations, Proc. Camb. Phil. Soc., 53 (1957), 778780.
J. Loy, The HardyRamanujan Number
Eric Weisstein's World of Mathematics, Cubic Number
Eric Weisstein's World of Mathematics, Diophantine Equation 3rd Powers
Eric Weisstein's World of Mathematics, Taxicab Number
D. W. Wilson, The Fifth Taxicab Number is 48988659276962496, J. Integer Sequences, Vol. 2, 1999, #99.1.9.


EXAMPLE

4104 belongs to the sequence as 4104 = 2^3 + 16^3 = 9^3 + 15^3.


MATHEMATICA

lst={}; q=1; k=1; Do[Do[x=a^3; Do[y=b^3; If[x+y==n, If[n==q&&k==1, AppendTo[lst, n]]; If[n!=q, q=n; k=1, k++ ]], {b, Floor[(nx)^(1/3)], a+1, 1}], {a, Floor[n^(1/3)], 1, 1}], {n, 2*6!, 8!}]; lst (* Vladimir Joseph Stephan Orlovsky, Jan 22 2009 *)
Select[Range[750000], Length[PowersRepresentations[#, 2, 3]]==2&] (* Harvey P. Dale, Nov 25 2014 *)


PROG

(PARI) is(n)=my(t); for(k=ceil((n/2)^(1/3)), (n.4)^(1/3), if(ispower(nk^3, 3), if(t, return(1), t=1))); 0 \\ Charles R Greathouse IV, Jul 15 2011


CROSSREFS

Cf. A011541, A018850, A003325, A003826, A023050, A023051.
Sequence in context: A182207 A138129 A242880 * A018850 A062924 A130859
Adjacent sequences: A001232 A001233 A001234 * A001236 A001237 A001238


KEYWORD

nonn,nice


AUTHOR

N. J. A. Sloane


STATUS

approved



