|
|
A136025
|
|
Sum of distinct proper prime divisors of odd integers below 10^n.
|
|
2
|
|
|
3, 373, 24307, 1691682, 127867801, 10233538789, 850896280551, 72812857079241, 6363727756215813, 565232434009370012, 50843507342073211151, 4620323131256374760046, 423405369424475640435621, 39074878176445767411791424
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
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.
|
|
LINKS
|
|
|
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
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|