Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #14 Aug 05 2023 22:37:16
%S 3774,5565,6726,8151,10659,10934,11726,11935,12426,13035,13195,13674,
%T 13755,14763,15042,15249,15351,15785,16215,16226,17630,17765,17974,
%U 17985,18249,18278,18915,18998,19565,20085,21385,21574,21855,22015,23023,23345,23374,23426,24038,24605,25185
%N Products k of 4 distinct primes (or tetraprimes) such that k has no squarefree neighbors.
%e 3773 = 7^3 * 11, 3774 = 2 * 3 * 17 * 37, 3775 = 5^2 * 151, so 3774 is a term.
%e 5564 = 2^2 * 13 * 107, 5565 = 3 * 5 * 7 * 53, 5566 = 2 * 11^2 * 23, so 5565 is a term.
%t Select[Range[26000], FactorInteger[#][[;; , 2]] == {1, 1, 1, 1} && ! SquareFreeQ[# - 1] && ! SquareFreeQ[# + 1] &] (* _Amiram Eldar_, Jul 10 2023 *)
%Y Cf. A013929, A046386.
%K nonn
%O 1,1
%A _Massimo Kofler_, Jul 10 2023