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A141767
A positive integer k is included if (p-1)*(p+1) divides k for every prime p that divides k.
4
1, 24, 48, 72, 96, 120, 144, 192, 216, 240, 288, 336, 360, 384, 432, 480, 576, 600, 648, 672, 720, 768, 864, 960, 1008, 1080, 1152, 1200, 1296, 1320, 1344, 1440, 1536, 1680, 1728, 1800, 1920, 1944, 2016, 2160, 2304, 2352, 2400, 2592, 2640, 2688, 2880, 3000
OFFSET
1,2
COMMENTS
For n>1, a(n) is a multiple of 24.
LINKS
EXAMPLE
120 has the prime factorization of 2^3 * 3^1 * 5^1. The distinct primes dividing 120 are therefore 2,3,5. (2-1)*(2+1)=3, (3-1)*(3+1)=8 and (5-1)*(5+1)=24 all divide 120. So 120 is included in the sequence.
MATHEMATICA
fQ[n_] := Block[{p = First /@ FactorInteger@ n}, Union@ Mod[n, (p - 1) (p + 1)] == {0}]; Select[ Range[2, 3000], fQ@# &] (* Robert G. Wilson v, May 25 2009 *)
PROG
(Haskell)
a141767 n = a141767_list !! (n-1)
a141767_list = filter f [1..] where
f x = all (== 0) $
map (mod x) $ zipWith (*) (map pred ps) (map succ ps)
where ps = a027748_row x
-- Reinhard Zumkeller, Aug 27 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Jul 02 2008
EXTENSIONS
Added missing term 336 and a(14)-a(47) from Donovan Johnson, Sep 27 2008
a(1)=1 prepended by Max Alekseyev, Aug 27 2013
STATUS
approved