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A002311
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Numbers k such that the k-th tetrahedral number is the sum of 2 tetrahedral numbers.
(Formerly M3498 N1419)
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7
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4, 15, 55, 58, 74, 109, 110, 119, 140, 175, 245, 294, 418, 435, 452, 474, 492, 528, 535, 550, 562, 588, 644, 688, 702, 714, 740, 747, 753, 818, 868, 908, 918, 1098, 1158, 1220, 1241, 1428, 1434, 1444, 1450, 1645, 1708, 1738, 1786, 1868, 2170, 2183, 2220, 2256
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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REFERENCES
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Aviezri S. Fraenkel, Diophantine equations involving generalized triangular and tetrahedral numbers, pp. 99-114 of A. O. L. Atkin and B. J. Birch, editors, Computers in Number Theory. Academic Press, NY, 1971.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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FORMULA
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MATHEMATICA
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With[{tetras=Binomial[Range[1100]+2, 3]}, Flatten[Position[tetras, #]&/@ Union[Select[Total/@Tuples[tetras, 2], MemberQ[tetras, #]&]]]] (* Harvey P. Dale, Jul 26 2011 *)
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PROG
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(Haskell)
import Data.List (intersect)
a002311 n = a002311_list !! (n-1)
a002311_list = filter f [1..] where
f x = not $ null $ intersect txs $ map (tx -) $ txs where
txs = takeWhile (< tx) a000292_list; tx = a000292 x
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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STATUS
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approved
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