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A066664 Composite numbers n whose divisors less than or equal to sqrt(n) are consecutive, from 1 up to some number k. 2
4, 6, 8, 10, 12, 14, 18, 22, 24, 26, 34, 38, 46, 58, 60, 62, 74, 82, 86, 94, 106, 118, 122, 134, 142, 146, 158, 166, 178, 194, 202, 206, 214, 218, 226, 254, 262, 274, 278, 298, 302, 314, 326, 334, 346, 358, 362, 382, 386, 394, 398, 422, 446, 454, 458, 466, 478 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
The sequence consists of all numbers of the form 2p with p prime, along with 8, 12, 18, 24 and 60. See sketch of proof in A066522.
LINKS
MATHEMATICA
a = {}; Do[ If[ !PrimeQ[n], k = Select[ Divisors[n], # <= Sqrt[n] &]; If[ Last[k] == Length[k], a = Append[a, n]]], {n, 1, 500} ]; a
dQ[n_]:=!PrimeQ[n]&&Union[Differences[Select[Divisors[n], #<=Sqrt[n]&]]] == {1}; Select[Range[500], dQ] (* Harvey P. Dale, Nov 06 2013 *)
PROG
(Haskell)
a066664 n = a066664_list !! (n-1)
a066664_list = filter ((== 0) . a010051) $ tail a066522_list
-- Reinhard Zumkeller, Nov 14 2011
CROSSREFS
These are the composite members of A066522: intersection of A002808 and A066522.
Subsequence: A100484.
Sequence in context: A258036 A242396 A061344 * A064938 A050990 A289425
KEYWORD
nice,nonn,easy
AUTHOR
Robert G. Wilson v, Jan 07 2002
STATUS
approved

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Last modified April 19 15:34 EDT 2024. Contains 371794 sequences. (Running on oeis4.)