A375964 Semiprime numbers that are sandwiched between products of exactly 4 distinct primes (or tetraprimes).

41614, 51358, 55166, 67066, 97054, 97294, 100834, 101914, 109838, 122758, 126634, 130646, 133286, 148394, 154582, 175594, 180214, 180454, 184666, 197086, 212486, 224258, 226654, 227446, 231386, 242906, 258446, 276394, 284866, 285086, 300182, 305066, 308606, 309506, 317054, 344434, 350206, 352834, 360634, 362594

Offset: 1

Author

Massimo Kofler, Sep 04 2024

Keywords

• nonn

Examples

			41614 = 2 * 20807 (between 41613 = 3*11*13*97 and 41615 = 5*7*29*41).
51358 = 2 * 25679 (between 51357 = 3*17*19*53 and 51359 = 7*11*23*29).
55166 = 2 * 27583 (between 55165 = 5*11*17*59 and 55167 = 3*7*37*71).
		

Crossrefs

Cf. A006881, A046386.

Subsequence of A100484.

Programs

Mathematica

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 *)

Formula

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