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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

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

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

Adjacent sequences:  A066661 A066662 A066663 * A066665 A066666 A066667

KEYWORD

nice,nonn,easy

AUTHOR

Robert G. Wilson v, Jan 07 2002

STATUS

approved

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Last modified September 28 06:57 EDT 2021. Contains 347703 sequences. (Running on oeis4.)