

A285120


Min(d(k+1i)  d(i), for i = 1..k, where d(1),..,d(k) are the divisors of n(n+1)/2.


1



0, 2, 1, 3, 2, 4, 3, 0, 4, 6, 5, 7, 6, 8, 2, 9, 8, 10, 9, 1, 10, 12, 11, 5, 12, 14, 3, 15, 14, 16, 15, 2, 16, 18, 9, 19, 18, 20, 4, 21, 20, 22, 21, 3, 22, 24, 23, 14, 0, 26, 5, 27, 26, 12, 9, 4, 28, 30, 29, 31, 30, 32, 6, 12, 16, 34, 33, 5, 34, 36, 35, 37
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OFFSET

1,2


LINKS

Clark Kimberling, Table of n, a(n) for n = 1..10000


FORMULA

a(n)=A056737(A000217(n)).


EXAMPLE

7(7+1)/2 = 28 has divisors 1,2,4,7,14,28, so that k=6 and d(k+1i)  d(i) ranges through {27,12,3,3,12,27}, so that a(7) = 3.


MATHEMATICA

f[n_] := f[n] = n(n+1)/2;
Table[Divisors[f[n]]  Reverse[Divisors[f[n]]], {n, 1, 10}]
Table[Min[Abs[Divisors[f[n]]  Reverse[Divisors[f[n]]]]], {n, 1, 100}]


CROSSREFS

Cf. A000217, A002378, A056737.
Sequence in context: A078658 A307719 A185314 * A282744 A195310 A051282
Adjacent sequences: A285117 A285118 A285119 * A285121 A285122 A285123


KEYWORD

nonn,easy


AUTHOR

Clark Kimberling, Apr 11 2017


STATUS

approved



