The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A248201 Numbers n such that n-1, n and n+1 are all squarefree semiprimes. 8
 34, 86, 94, 142, 202, 214, 218, 302, 394, 446, 634, 698, 922, 1042, 1138, 1262, 1346, 1402, 1642, 1762, 1838, 1894, 1942, 1982, 2102, 2182, 2218, 2306, 2362, 2434, 2462, 2518, 2642, 2722, 2734, 3098, 3386, 3602, 3694, 3866, 3902, 3958, 4286, 4414 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A subsequence of A169834. - M. F. Hasler, Oct 26 2014 LINKS Giovanni Resta, Table of n, a(n) for n = 1..10000 Wikipedia, Semiprime FORMULA a(n) = A039833(n) + 1. - Michel Marcus, Oct 25 2014 EXAMPLE 33, 34 and 35 factor as 3*11, 2*17 and 5*7, respectively.  No smaller such trio exists, so a(1)=34. MATHEMATICA lst={}; Do[z=n^3 + 3 n^2 + 2 n; If[PrimeOmega[z/n]==PrimeOmega[z/(n + 2)]==4 && PrimeNu[z]==6, AppendTo[lst, n + 1]], {n, 1, 6000, 2}]; lst (* Vincenzo Librandi, Jul 24 2015 *) SequencePosition[Table[If[SquareFreeQ[n]&&PrimeOmega[n]==2, 1, 0], {n, 4500}], {1, 1, 1}][[All, 1]]+1 (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 11 2018 *) PROG (PARI) sq(n)=bigomega(n)==2 && omega(n)==2; for(n=3, 10^4, if(sq(n-1)&&sq(n)&&sq(n+1), print1(n, ", "))); \\ Joerg Arndt, Oct 18 2014 CROSSREFS Cf. A039833, A169834, A006881, A248202, A248203, A248204, A259349, A259350, A259801. Sequence in context: A213025 A086005 A169834 * A140602 A067977 A183311 Adjacent sequences:  A248198 A248199 A248200 * A248202 A248203 A248204 KEYWORD nonn AUTHOR James G. Merickel, Oct 03 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 21 19:16 EDT 2021. Contains 343156 sequences. (Running on oeis4.)