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A138798 Values of j corresponding to least possible k>0 with T(k)-T(j)=n, where T(i)>0 are the triangular numbers A000217. 3
1, 2, 3, 1, 5, 2, 7, 1, 9, 4, 2, 5, 1, 3, 15, 7, 2, 8, 1, 5, 3, 10, 6, 2, 4, 1, 27, 13, 3, 14, 31, 2, 6, 1, 10, 17, 7, 3, 5, 19, 2, 20, 1, 4, 9, 22, 14, 3, 7, 5, 2, 25, 1, 8, 4, 6, 12, 28, 3, 29, 13, 2, 63, 1, 14, 32, 4, 8, 6, 34, 3, 35, 16, 2, 5, 1, 17, 38, 13, 4, 18, 40, 6, 3, 19, 11, 2, 43, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

COMMENTS

For k see A138796, for T(k) see A138797 and for T(j) see A138799.

The number of ways n can be written as difference of two triangular numbers is sequence A136107

LINKS

Table of n, a(n) for n=2..90.

EXAMPLE

a(30)=3 because 30 = T(30)-T(29)=T(11)-T(8)=T(9)-T(5)=T(8)-T(3) and 3 is the least index of the subtrahends.

MATHEMATICA

T=#(#+1)/2&; Sort[{k, j}/.{ToRules[Reduce[{T[k]-T[j]\[Equal]#, 0<j<k}, {j, k}, Integers]]}][[1, 2]]&/@Range[2, 100]

CROSSREFS

Cf. A000217, A109814, A118235, A136107, A138796, A138797, A138799.

Sequence in context: A308707 A158584 A086112 * A277708 A261555 A134734

Adjacent sequences:  A138795 A138796 A138797 * A138799 A138800 A138801

KEYWORD

nonn

AUTHOR

Peter Pein (petsie(AT)dordos.net), Mar 30 2008

STATUS

approved

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Last modified October 15 04:33 EDT 2019. Contains 328026 sequences. (Running on oeis4.)