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.
%I A380937 #24 Apr 18 2025 21:17:11
%S A380937 288,392,1944,4500,4608,7200,9248,13068,14112,14792,16200,18000,19652,
%T A380937 21632,26136,26912,28800,31104,32000,34992,38088,38988,41472,42592,
%U A380937 45000,48668,49000,52272,55112,56448,60552,69984,78732,79092,87808,88200,95832,98568
%N A380937 Achilles numbers sandwiched between two semiprimes.
%C A380937 Achilles numbers are powerful but imperfect.
%C A380937 All the terms are divisible by 4.
%e A380937 288 = 2^5 * 3^2 (between 287 = 7 * 41 and 289 = 17^2).
%e A380937 392 = 2^3 * 7^2 (between 391 = 17 * 23 and 393 = 3 * 131).
%e A380937 1944 = 2^3 * 3^5 (between 1943 = 29 * 67 and 1945 = 5 * 389).
%t A380937 achQ[n_] := Module[{e = FactorInteger[n][[;; , 2]]}, Min[e] > 1 && GCD @@ e == 1]; semiQ[n_] := PrimeOmega[n] == 2; Select[4*Range[25000], achQ[#] && And @@ semiQ /@ (# + {-1, 1}) &] (* _Amiram Eldar_, Apr 12 2025 *)
%Y A380937 Cf. A001358, A052486, A382831.
%K A380937 nonn
%O A380937 1,1
%A A380937 _Massimo Kofler_, Apr 12 2025