| 2, 3, 4, 3, 6, 4, 8, 4, 10, 6, 5, 7, 5, 6, 16, 9, 6, 10, 6, 8, 7, 12, 9, 7, 8, 7, 28, 15, 8, 16, 32, 8, 10, 8, 13, 19, 11, 9, 10, 21, 9, 22, 9, 10, 13, 24, 17, 10, 12, 11, 10, 27, 10, 13, 11, 12, 16, 30, 11, 31, 17, 11, 64, 11, 18, 34, 12, 14, 13, 36, 12, 37, 20, 12, 13, 12, 21, 40, 18
(list; graph; listen)
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OFFSET
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2,1
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COMMENT
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For T(k) see A138797, for j see A138798 and for T(j) see A138799.
The number of ways n can be written as difference of two triangular numbers is sequence A136107
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LINKS
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Peter Pein, Mathematica notebook containing a faster algorithm.
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EXAMPLE
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a(30)=8, because 30 = T(30)-T(29)=T(11)-T(8)=T(9)-T(5)=T(8)-T(3) and 8 is the least index of the minuends
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MATHEMATICA
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T=#(#+1)/2&; Min[k/.{ToRules[Reduce[{T[k]-T[j]\[Equal]#, 0<j<k}, {j, k}, Integers]]}]&/@Range[2, 100]
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CROSSREFS
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Cf. A000217, A109814, A118235, A136107, A138797, A138798, A138799.
Sequence in context: A126630 A167234 A088043 this_sequence A064380 A126214 A126801
Adjacent sequences: A138793 A138794 A138795 this_sequence A138797 A138798 A138799
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KEYWORD
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nonn
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AUTHOR
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Peter Pein (petsie(AT)dordos.net), Mar 30, 2008
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