A105573 Numbers m such that m-4 and m+4 have 4 prime factors.

20, 136, 200, 224, 344, 346, 368, 376, 480, 488, 554, 568, 576, 640, 736, 744, 808, 816, 854, 856, 864, 872, 880, 944, 992, 1064, 1152, 1160, 1200, 1208, 1214, 1216, 1280, 1288, 1312, 1360, 1426, 1568, 1576, 1606, 1621, 1648, 1656, 1664, 1784, 1808, 1858

Offset

1,1

Comments

A001222(a(n)-4) = A001222(a(n)+4) = 4.

Prime factors counted with multiplicity. - Harvey P. Dale, Feb 06 2020

Links

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

Example

1214 - 4 = 1210 = 2 * 5 * 11 * 11 and 1214 + 4 = 1218 = 2 * 3 * 7 * 29 so 1214 is in the sequence. - Jon E. Schoenfield, Jan 19 2015

Mathematica

q=4; 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 *)
Mean/@SequencePosition[PrimeOmega[Range[2000]], {4, _, _, _, _, _, _, _, 4}] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Feb 06 2020 *)

Crossrefs

Cf. A014574, A105571, A105572.

Sequence in context: A188145 A168178 A085284 * A144965 A262140 A140301

Adjacent sequences: A105570 A105571 A105572 * A105574 A105575 A105576

Keyword

nonn

Author

Reinhard Zumkeller, Apr 14 2005

Status

approved