cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A364025 Semiprimes with no squarefree neighbors.

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%I A364025 #21 Dec 16 2023 09:00:43
%S A364025 26,49,51,55,91,161,235,249,295,305,339,341,362,377,413,415,451,485,
%T A364025 489,551,559,579,629,649,667,685,687,703,721,723,737,749,849,851,917,
%U A364025 926,949,951,955,989,1027,1057,1059,1077,1079,1099,1126,1133,1135,1149,1169,1205,1207,1211,1241
%N A364025 Semiprimes with no squarefree neighbors.
%H A364025 Robert Israel, <a href="/A364025/b364025.txt">Table of n, a(n) for n = 1..10000</a>
%e A364025 25 = 5^2, 26 = 2 * 13, 27 = 3^3, so 26 is a term.
%e A364025 50 = 2 * 5^2, 51 = 3 * 17, 52 = 2^2 * 13, so 51 is a term.
%p A364025 filter:= proc(n) uses numtheory; not issqrfree(n-1) and not issqrfree(n+1) and bigomega(n) = 2 end proc:
%p A364025 selest(filter, [$1..2000]); # _Robert Israel_, Dec 12 2023
%t A364025 Select[Range[1300], PrimeOmega[#] == 2 && ! AnyTrue[# + {-1, 1}, SquareFreeQ] &] (* _Amiram Eldar_, Jul 01 2023 *)
%o A364025 (PARI) isok(k) = (bigomega(k)==2) && !issquarefree(k-1) && !issquarefree(k+1); \\ _Michel Marcus_, Aug 12 2023
%Y A364025 Intersection of A001358 and A281192.
%Y A364025 Cf. A013929, A364010.
%K A364025 nonn
%O A364025 1,1
%A A364025 _Massimo Kofler_, Jul 01 2023