|
| |
|
|
A078730
|
|
Sum of products of two successive divisors of n.
|
|
1
| |
|
|
0, 2, 3, 10, 5, 26, 7, 42, 30, 62, 11, 116, 13, 114, 93, 170, 17, 242, 19, 280, 171, 266, 23, 476, 130, 366, 273, 528, 29, 713, 31, 682, 399, 614, 285, 1070, 37, 762, 549, 1150, 41, 1342, 43, 1264, 873, 1106, 47, 1916, 350, 1562, 921, 1752, 53, 2186, 665, 2166, 1143
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,2
|
|
|
COMMENTS
| a(n) = dot_product (d_1,d_2,...,d_(tau(n)-1))*(d_2,d_3,...d_tau(n)), where d_1<d_2<...<d_tau(n), is increasing sequence of divisors of n. a(10) = dot_product (1,2,5)*(2,5,10) = 2+10+50 = 62.
|
|
|
MATHEMATICA
| f[n_] := Module[{d, l, s, i}, d = Divisors[n]; l = Length[d]; s = 0; For[i = 1, i < l, i++, s = s + d[[i + 1]]*d[[i]]]; s]; Table[ f[n], {n, 1, 100}]
|
|
|
CROSSREFS
| Cf. A078713(n) = 2*A001157(n)-2*a(n)-n^2-1.
Sequence in context: A139693 A175899 A064946 * A163767 A128531 A123167
Adjacent sequences: A078727 A078728 A078729 * A078731 A078732 A078733
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Dec 20 2002
|
| |
|
|
