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A002311
Numbers k such that the k-th tetrahedral number is the sum of 2 tetrahedral numbers.
(Formerly M3498 N1419)
7
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
OFFSET
1,1
COMMENTS
Indices of A034404. - Harvey P. Dale, Jul 25 2011
REFERENCES
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).
LINKS
M. Wunderlich, Certain properties of pyramidal and figurate numbers, Math. Comp., 16 (1962), 482-486.
FORMULA
a(n) = A010330(n) - 2. - Reinhard Zumkeller, May 02 2014
MATHEMATICA
With[{tetras=Binomial[Range[1100]+2, 3]}, Flatten[Position[tetras, #]&/@ Union[Select[Total/@Tuples[tetras, 2], MemberQ[tetras, #]&]]]] (* Harvey P. Dale, Jul 26 2011 *)
PROG
(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
-- Reinhard Zumkeller, May 02 2014
CROSSREFS
KEYWORD
nonn,easy,nice
STATUS
approved