OFFSET
1,1
COMMENTS
Through 10^5 about 37.5% of total sums for all integers N comprise sums of odd N and the remaining 62.5% of even N.
FORMULA
a(n) = sum_{prime p, 3<=p<10^n} p*floor((10^n-p)/(2p)). - Max Alekseyev, Jan 30 2012
EXAMPLE
a(0)=3 because the only odd N <=10^1-1 having a prime factor is 9 and its factor is 3 and sum is 3.
MAPLE
A105221 := proc(n) local a, ifs, p; ifs := ifactors(n)[2] ; a := 0 ; for p in ifs do if op(1, p) <> 1 and op(1, p) <> n then a := a+op(1, p) ; fi ; od: RETURN(a) ; end: A136025 := proc(n) local a, k ; a := 0 ; for k from 5 to 10^n-1 by 2 do a := a+A105221(k) ; od: RETURN(a) ; end: for n from 1 do print(A136025(n)); od: # R. J. Mathar, Jan 29 2008
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Enoch Haga, Dec 12 2007
EXTENSIONS
a(6) from R. J. Mathar, Jan 29 2008
a(7)-a(11) from Max Alekseyev, Jan 30 2012
a(12)-a(14) from Hiroaki Yamanouchi, Jul 06 2014
STATUS
approved