login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A131484 Numbers n such that A001414(n) divides n+1 and A001414(n+1) divides n. 1
44, 41005, 41040, 68263, 91907, 109736, 416325, 603954, 826987, 1122407, 1218999, 1262079, 1533375, 1649375, 1835584, 1935225, 1964199, 2141888, 2562016, 2615799, 2649352, 3021075, 3186000, 3554880, 3863678, 4221536, 4655805, 4925844, 5236153, 5273100 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

There is remote formal resemblance to amicable pairs.

LINKS

Klaus Brockhaus and Donovan Johnson, Table of n, a(n) for n = 1..1000 (first 126 terms from Klaus Brockhaus)

EXAMPLE

44 = 2*2*11 has sum of prime factors 15, which divides 44 + 1 = 45; 45 = 3*3*5 has sum of prime factors 11, which divides 44. Hence 44 is in the sequence.

PROG

(PARI) {m=4700000; s=2; for(n=2, m, f=factor(n+1); t=sum(j=1, matsize(f)[1], f[j, 1]*f[j, 2]); if((n+1)%s==0&&n%t==0, print1(n, ", ")); s=t)} /* Klaus Brockhaus, Jul 30 2007 */

CROSSREFS

Cf. A001414 (sum of prime factors of n, with repetition), A063990 (amicable numbers), A130871.

Sequence in context: A268425 A183749 A119096 * A308325 A305997 A277840

Adjacent sequences:  A131481 A131482 A131483 * A131485 A131486 A131487

KEYWORD

nonn

AUTHOR

J. M. Bergot, Jul 28 2007

EXTENSIONS

Edited and extended by Stefan Steinerberger and Klaus Brockhaus, Jul 30 2007

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 9 13:09 EDT 2021. Contains 343742 sequences. (Running on oeis4.)