login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A318737 Numbers n=2*k-1 where Sum_{j=1..k} (-1)^(j+1) * d(2*j-1) achieves a new record, with d(n) = number of divisors of n (A000005). 5
1, 9, 25, 49, 85, 133, 169, 225, 445, 845, 973, 1125, 2205, 2209, 2469, 2829, 7929, 9429, 9945, 23569, 24073, 24645, 26145, 40425, 68153, 71289, 72413, 89517, 112233, 112245, 128973, 162405, 162409, 162429, 297073, 477489, 477493, 502713, 561253 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Hugo Pfoertner, Table of n, a(n) for n = 1..268

EXAMPLE

a(2) = 9, because s = d(1)-d(3)+d(5)-d(7)+d(9) = 1-2+2-2+3 = 2 exceeds d(1)=1, d(1)-d(3)=-1, d(1)-d(3)+d(5)=1, d(1)-d(3)+d(5)-d(7)=-1.

PROG

(PARI) s=0; smax=0; j=-1; forstep(k=1, 600000, 2, j=-j; s=s+j*numdiv(k); if(s>smax, smax=s; print1(k, ", ")))

CROSSREFS

Cf. A000005, A099774, A318734, A318735, A318736, A318738.

Sequence in context: A259417 A030156 A192775 * A246331 A141768 A176970

Adjacent sequences:  A318734 A318735 A318736 * A318738 A318739 A318740

KEYWORD

nonn

AUTHOR

Hugo Pfoertner, Sep 05 2018

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 21 10:48 EDT 2019. Contains 323443 sequences. (Running on oeis4.)