A367791 Lesser of 2 successive tetraprimes (k, k+4) sandwiching three consecutive not squarefree numbers.

3770, 12122, 12426, 17574, 19158, 22074, 28574, 31506, 40922, 46322, 47382, 50930, 52854, 57174, 60378, 61586, 66174, 72474, 74222, 77231, 78774, 85074, 85526, 87954, 89090, 91322, 91374, 95226, 97622, 99582, 104210, 106674, 113734, 118374, 120786, 122822, 124674, 126870, 127673

Offset

1,1

Comments

Tetraprimes are the product of four distinct prime numbers (cf. A046386).

Links

Table of n, a(n) for n=1..39.

Example

3770 = 2*5*13*29, 3771 = 3^2*419, 3772 = 2^2*23*41, 3773 = 7^3*11, 3774 = 2*3*17*37, so 3770 is a term.
12122 = 2*11*19*29, 12123 = 3^3*449, 12124 = 2^2*7*433, 12125 = 5^3*97, 12126 = 2*3*43*47, so 12122 is a term.

Mathematica

f[n_] := Module[{e = FactorInteger[n][[;; , 2]]}, If[e == {1, 1, 1, 1}, 1, If[AnyTrue[e, # > 1 &], 2, 0]]]; Position[Partition[Array[f, 130000], 5, 1], {1, 2, 2, 2, 1}][[;; , 1]] (* Amiram Eldar, Nov 30 2023 *)

Crossrefs

Cf. A046386, A013929.

Sequence in context: A284079 A108179 A336584 * A364141 A364766 A080953

Adjacent sequences: A367788 A367789 A367790 * A367792 A367793 A367794

Keyword

nonn

Author

Massimo Kofler, Nov 30 2023

Status

approved