OFFSET
1,3
COMMENTS
Sum of the largest proper divisors of all positive integers <= n.
LINKS
Eric Weisstein's World of Mathematics, Proper Divisor
Eric Weisstein's World of Mathematics, Least Prime Factor
FORMULA
EXAMPLE
For n = 8 the divisors of the first eight positive integers are {1}, {1, 2}, {1, 3}, {1, 2, 4}, {1, 5}, {1, 2, 3, 6}, {1, 7}, {1, 2, 4, 8}, so a(8) = 1 + 1 + 2 + 1 + 3 + 1 + 4 = 13.
MATHEMATICA
Table[Sum[k/FactorInteger[k][[1, 1]], {k, 2, n}], {n, 71}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Ilya Gutkovskiy, Jan 02 2017
STATUS
approved