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Search: id:A020894
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| A020894 |
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Sum of two nonzero cubes. |
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+0
2
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| 2, 7, 9, 16, 19, 26, 28, 35, 37, 54, 56, 61, 63, 65, 72, 91, 98, 117, 124, 126, 127, 128, 133, 152, 169, 189, 208, 215, 217, 218, 224, 243, 250, 271, 279, 280, 296, 316, 331, 335, 341, 342, 344, 351, 370, 386, 387, 397, 407, 432, 448, 468, 469
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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Contribution from Michael Porter (michael_b_porter(AT)yahoo.com), Oct 16 2009: (Start)
When calculating terms, there is no need to search beyond a value x defined by x^3 - (x-1)^3 = n. The positive solution is given by x = 1/2 + (sqrt(12n-3))/6.
There are no cubes in this sequence, but the numbers before and after a cube are all included. (End)
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LINKS
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S. R. Finch, On a Generalized Fermat-Wiles Equation
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EXAMPLE
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Contribution from Michael Porter (michael_b_porter(AT)yahoo.com), Oct 16 2009: (Start)
7 is in the sequence because 2^3 + (-1)^3 = 7
8 is not in the sequence because the only solutions to x^3 + y^3 = 8 have either x=0 or y=0. (End)
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PROGRAM
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(PARI) isA020894(n) = {r=0; x=1.0/2+sqrt(12*n-3.0)/6; for(i=1, floor(x), if(ispower(n-i^3, 3) & (n != i^3), r++)); r>0}; [From Michael Porter (michael_b_porter(AT)yahoo.com), Oct 16 2009]
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CROSSREFS
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Cf. A045980 [From Michael Porter (michael_b_porter(AT)yahoo.com), Oct 16 2009]
Sequence in context: A154789 A106352 A098017 this_sequence A165995 A022113 A041643
Adjacent sequences: A020891 A020892 A020893 this_sequence A020895 A020896 A020897
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KEYWORD
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nonn
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AUTHOR
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Steven.Finch(AT)inria.fr (S. R. Finch)
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