A131484 Numbers n such that A001414(n) divides n+1 and A001414(n+1) divides n.

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

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 * A365646 A308325 A305997

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