A105572 Numbers m such that m-3 and m+3 have 3 prime factors.

15, 47, 73, 95, 102, 113, 127, 150, 151, 167, 168, 185, 233, 239, 241, 258, 276, 282, 287, 289, 313, 319, 335, 360, 366, 407, 409, 415, 426, 431, 432, 433, 439, 480, 521, 527, 552, 558, 593, 599, 601, 606, 607, 612, 642, 648, 649, 654, 655, 660, 708, 713

Offset

1,1

Comments

A001222(a(n)-3) = A001222(a(n)+3) = 3.

Prime factors counted with multiplicity. - Harvey P. Dale, May 07 2023

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

From Jon E. Schoenfield, Jan 19 2015: (Start)
73 - 3 = 70 = 2 * 5 * 7 and 73 + 3 = 76 = 2 * 2 * 19 so 73 is in the sequence.
81 - 3 = 78 = 2 * 3 * 13 but 81 + 3 = 84 = 2 * 2 * 3 * 7 so 81 is not in the sequence. (End)

Mathematica

q=3; lst={}; Do[If[Plus@@Last/@FactorInteger[n-q]==q&&Plus@@Last/@FactorInteger[n+q]==q, AppendTo[lst, n]], {n, 7!}]; lst (* Vladimir Joseph Stephan Orlovsky, Feb 01 2009 *)
Flatten[Position[Partition[PrimeOmega[Range[800]], 7, 1], _?(#[[1]]==#[[7]]==3&), 1, Heads-> False]]+3 (* Harvey P. Dale, May 07 2023 *)

Crossrefs

Cf. A014574, A105571, A105573.

Sequence in context: A041438 A045111 A031451 * A143031 A214675 A166118

Adjacent sequences: A105569 A105570 A105571 * A105573 A105574 A105575

Keyword

nonn

Author

Reinhard Zumkeller, Apr 14 2005

Status

approved