A375964 - OEIS

%I #14 Sep 20 2024 06:27:06

%S 41614,51358,55166,67066,97054,97294,100834,101914,109838,122758,

%T 126634,130646,133286,148394,154582,175594,180214,180454,184666,

%U 197086,212486,224258,226654,227446,231386,242906,258446,276394,284866,285086,300182,305066,308606,309506,317054,344434,350206,352834,360634,362594

%N Semiprime numbers that are sandwiched between products of exactly 4 distinct primes (or tetraprimes).

%F a(n) == 2 (mod 4).

%e 41614 = 2 * 20807 (between 41613 = 3*11*13*97 and 41615 = 5*7*29*41).

%e 51358 = 2 * 25679 (between 51357 = 3*17*19*53 and 51359 = 7*11*23*29).

%e 55166 = 2 * 27583 (between 55165 = 5*11*17*59 and 55167 = 3*7*37*71).

%t e[n_] := FactorInteger[n][[;; , 2]]; SequencePosition[e /@ Range[400000], {{1, 1, 1, 1}, {1, 1}, {1, 1, 1, 1}}][[;; , 1]] + 1 (* _Amiram Eldar_, Sep 04 2024 *)

%Y Cf. A006881, A046386.

%Y Subsequence of A100484.

%K nonn

%O 1,1

%A _Massimo Kofler_, Sep 04 2024