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A364025 Semiprimes with no squarefree neighbors. 3
26, 49, 51, 55, 91, 161, 235, 249, 295, 305, 339, 341, 362, 377, 413, 415, 451, 485, 489, 551, 559, 579, 629, 649, 667, 685, 687, 703, 721, 723, 737, 749, 849, 851, 917, 926, 949, 951, 955, 989, 1027, 1057, 1059, 1077, 1079, 1099, 1126, 1133, 1135, 1149, 1169, 1205, 1207, 1211, 1241 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
25 = 5^2, 26 = 2 * 13, 27 = 3^3, so 26 is a term.
50 = 2 * 5^2, 51 = 3 * 17, 52 = 2^2 * 13, so 51 is a term.
MAPLE
filter:= proc(n) uses numtheory; not issqrfree(n-1) and not issqrfree(n+1) and bigomega(n) = 2 end proc:
selest(filter, [$1..2000]); # Robert Israel, Dec 12 2023
MATHEMATICA
Select[Range[1300], PrimeOmega[#] == 2 && ! AnyTrue[# + {-1, 1}, SquareFreeQ] &] (* Amiram Eldar, Jul 01 2023 *)
PROG
(PARI) isok(k) = (bigomega(k)==2) && !issquarefree(k-1) && !issquarefree(k+1); \\ Michel Marcus, Aug 12 2023
CROSSREFS
Intersection of A001358 and A281192.
Sequence in context: A118367 A316120 A261932 * A324041 A137263 A073249
KEYWORD
nonn
AUTHOR
Massimo Kofler, Jul 01 2023
STATUS
approved

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Last modified July 16 12:01 EDT 2024. Contains 374348 sequences. (Running on oeis4.)