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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).
2
74431, 71528191, 125780831, 178708831, 4150390625, 68738591551, 171739186591, 429079903231, 634061169071
OFFSET
1,1
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
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