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A138799
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Values of T(j) corresponding to least possible T(k) with T(k)-T(j)=n, where T(i)>0 are the triangular numbers A000217.
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3
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1, 3, 6, 1, 15, 3, 28, 1, 45, 10, 3, 15, 1, 6, 120, 28, 3, 36, 1, 15, 6, 55, 21, 3, 10, 1, 378, 91, 6, 105, 496, 3, 21, 1, 55, 153, 28, 6, 15, 190, 3, 210, 1, 10, 45, 253, 105, 6, 28, 15, 3, 325, 1, 36, 10, 21, 78, 406, 6, 435, 91, 3, 2016, 1, 105, 528, 10, 36, 21, 595, 6, 630
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,2
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COMMENTS
| For k see A138796, for T(k) see A138797 and for j see A138798.
The number of ways n can be written as difference of two triangular numbers is sequence A136107
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EXAMPLE
| a(30)=6 because 30 = T(30)-T(29)=T(11)-T(8)=T(9)-T(5)=T(8)-T(3) and T(3)=6 is the least minuend.
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MATHEMATICA
| T=#(#+1)/2&; T[Sort[{k, j}/.{ToRules[Reduce[{T[k]-T[j]\[Equal]#, 0<j<k}, {j, k}, Integers]]}][[1, 2]]]&/@Range[2, 100]
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CROSSREFS
| Cf. A000217, A109814, A118235, A136107, A138796, A138797, A138798.
Sequence in context: A123534 A100960 A130852 * A108441 A176231 A176230
Adjacent sequences: A138796 A138797 A138798 * A138800 A138801 A138802
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KEYWORD
| nonn
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AUTHOR
| Peter Pein (petsie(AT)dordos.net), Mar 30, 2008
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