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A187204
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Numbers n such that the bottom entry in the difference table of the divisors of n is 0.
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9
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OFFSET
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1,1
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COMMENTS
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Numbers n such that A187202(n) = 0.
11373118351 and 1756410942451 are also in the sequence (not necessarily the next two terms). - Donovan Johnson, Aug 05 2011
a(9) > 6*10^10. 138662735650982521 and 168248347462416481 are also terms. - Giovanni Resta, Apr 12 2017
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LINKS
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EXAMPLE
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10 has divisors 1, 2, 5, 10. The third difference of these numbers is 0. This is the only possible number having 2 prime factors of the form p*q. The other terms have factorization 171 = 3^2*19, 1947 = 3*11*59, 2619 = 3^3*97, and 265105 = 5*37*1433.
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MATHEMATICA
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t = {}; Do[d = Divisors[n]; If[Differences[d, Length[d]-1] == {0}, AppendTo[t, n]], {n, 10^4}]; t (* T. D. Noe, Aug 01 2011 *)
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PROG
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(Haskell)
import Data.List (elemIndices)
a187204 n = a187204_list !! (n-1)
a187204_list = map (+ 1) $ elemIndices 0 $ map a187202 [1..]
(PARI) is(n) = my(d=divisors(n)); !sum(i=1, #d, binomial(#d-1, i-1)*d[i]*(-1)^i) \\ David A. Corneth, Apr 08 2017
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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