This site is supported by donations to The OEIS Foundation.

 Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A141800 For n>=2, a(n) = sum{k=1 to n} (smallest prime dividing (n*k)). a(1)=0. 2
 0, 4, 8, 8, 17, 12, 28, 16, 23, 20, 50, 24, 67, 28, 38, 32, 95, 36, 118, 40, 53, 44, 152, 48, 81, 52, 68, 56, 201, 60, 236, 64, 83, 68, 112, 72, 293, 76, 98, 80, 345, 84, 392, 88, 113, 92, 450, 96, 185, 100, 128, 104, 525, 108, 176, 112, 143, 116, 604, 120, 669, 124, 158 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Diana Mecum, Table of n, a(n) for n=1,...,1000 EXAMPLE For n = 5, the smallest prime dividing 1*5=5 is 5. The smallest prime dividing 2*5=10 is 2. The smallest prime dividing 3*5=15 is 3. The smallest prime dividing 4*5=20 is 2. And the smallest prime dividing 5*5=25 is 5. So a(5) = 5+2+3+2+5 = 17. MATHEMATICA Contribution from Diana L. Mecum, Jan 02 2009: (Start) Table[sum=0; Do[sum=sum+Min[Divisors[k*n][[2]], Divisors[n][[2]]], {k, 1, n}]; sum, {n, 2, 1000}], (then manually add in a(0)term) (End) CROSSREFS Cf. A141801. Sequence in context: A209382 A298119 A089474 * A019197 A066106 A030296 Adjacent sequences:  A141797 A141798 A141799 * A141801 A141802 A141803 KEYWORD nonn AUTHOR Leroy Quet, Jul 05 2008 EXTENSIONS Added terms a(10) - a(1000) Diana L. Mecum, Jan 02 2009 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 12 00:07 EST 2018. Contains 318052 sequences. (Running on oeis4.)