A079543 Numbers n such that n has at least two distinct prime factors and if a prime p divides n then (p-1) | (n-1) and (p+1) | (n+1).

74431, 71528191, 125780831, 178708831, 4150390625, 68738591551, 171739186591, 429079903231, 634061169071

Offset

1,1

Links

Table of n, a(n) for n=1..9.

Donovan Johnson, 1384 terms > a(9)

Example

a(1) = 74431 = 7^4 * 31 because 6 and 30 divide 74430 and 8 and 32 divide 74432.

Mathematica

Do[ f = Transpose[ FactorInteger[n]][[1]]; If[ Length[f] > 1 && Union[ Mod[n - 1, f - 1]] == {0} && Union[ Mod[n + 1, f + 1]] == {0}, Print[n]], {n, 6, 10^10}]

Crossrefs

Intersection of A056729 and A080062.

Sequence in context: A186835 A239587 A122065 * A033450 A033448 A234725

Adjacent sequences: A079540 A079541 A079542 * A079544 A079545 A079546

Keyword

nonn

Author

Don Reble, Jan 22 2003

Extensions

a(6)-a(7) from Donovan Johnson, Apr 09 2010

a(8)-a(9) from Donovan Johnson, Jan 21 2013

Status

approved