OFFSET
1,1
FORMULA
a(n) = (7/81)*(10^(n+1) - 9*n - 10). - R. Piyo (nagoya314(AT)yahoo.com), Dec 10 2004
EXAMPLE
7 + 77 + 777 + 7777 + 77777 = a(5) = 86415.
MATHEMATICA
<<NumberTheory`NumberTheoryFunctions` Table[{k, Table[Apply[Plus, Table[k*(10^n-1)/9, {n, 1, m}]], {m, 1, 35}]}, {k, 1, 9}]
Table[8/9*Sum[10^i - 1, {i, n}], {n, 18}] (* Robert G. Wilson v, Nov 20 2004 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Labos Elemer, Nov 17 2004
STATUS
approved