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A174653 Semiprimes s such that neither s-1 nor s+1 is semiprime. 1
4, 6, 46, 49, 51, 55, 62, 65, 69, 74, 77, 82, 91, 106, 111, 115, 129, 155, 161, 166, 169, 183, 185, 187, 194, 209, 221, 226, 235, 237, 247, 249, 259, 262, 265, 267, 274, 278, 287, 289, 291, 295, 305, 309, 314, 319, 321, 323, 329, 339, 341, 346, 355, 358, 365 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A064911(a(n))*(1 - A064911(a(n)-1))*(1 - A064911(a(n)+1)) = 1. - Reinhard Zumkeller, Apr 03 2010

LINKS

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

EXAMPLE

a(1)=4 because 4-1 = 3 (not semiprime) and 4+1 = 5 (not semiprime).

MATHEMATICA

Mean/@SequencePosition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 400}], {0, 1, 0}] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 19 2019 *)

CROSSREFS

Cf. A001358, A100959.

Sequence in context: A077100 A012935 A013166 * A274215 A119944 A338814

Adjacent sequences:  A174650 A174651 A174652 * A174654 A174655 A174656

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Mar 25 2010

EXTENSIONS

Corrected by Reinhard Zumkeller and Ray Chandler, Apr 07 2010

STATUS

approved

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Last modified September 25 12:12 EDT 2022. Contains 356984 sequences. (Running on oeis4.)