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A135545
a(n) = the largest proper divisor k of n where (k-1) and/or (k+1) divides (n+1).
1
1, 2, 1, 2, 1, 4, 3, 2, 1, 2, 1, 2, 5, 2, 1, 2, 1, 4, 3, 2, 1, 6, 1, 2, 3, 2, 1, 2, 1, 4, 3, 2, 7, 2, 1, 2, 3, 2, 1, 2, 1, 4, 3, 2, 1, 8, 1, 2, 3, 2, 1, 6, 5, 4, 3, 2, 1, 2, 1, 2, 9, 4, 5, 2, 1, 4, 3, 2, 1, 2, 1, 2, 5, 2, 7, 2, 1, 10, 3, 2, 1, 6, 1, 2, 3, 2, 1, 6, 1, 4, 3, 2, 5, 2, 1, 2, 11, 2
OFFSET
3,2
LINKS
EXAMPLE
The proper divisors of 14 are 1,2,7. Now 2 is the largest of these divisors k where (k-1) and/or (k+1) divides 15 -- both (2-1) and (2+1) divide 15. So a(14) = 2.
MATHEMATICA
Table[Max[Join[{1}, Select[Complement[Divisors[n], {1, n}], Mod[n + 1, # + 1] == 0 || Mod[n + 1, # - 1] == 0 &]]], {n, 3, 100}] (* Stefan Steinerberger, Aug 30 2008 *)
CROSSREFS
Sequence in context: A352933 A372598 A276976 * A123317 A231557 A171453
KEYWORD
nonn
AUTHOR
Leroy Quet, May 10 2008
EXTENSIONS
More terms from Stefan Steinerberger, Aug 30 2008
STATUS
approved