login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A195106 Numbers with largest and smallest prime factors differing by 4. 3
21, 63, 77, 105, 147, 189, 221, 315, 437, 441, 525, 539, 567, 735, 847, 945, 1029, 1323, 1517, 1575, 1701, 2021, 2205, 2625, 2835, 2873, 3087, 3675, 3757, 3773, 3969, 4725, 4757, 5103, 5145, 5929, 6557, 6615, 7203, 7875, 8303, 8505, 9261, 9317, 9797, 10051 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..250

Eric Weisstein's World of Mathematics, Cousin Primes

EXAMPLE

a(10) = 441 = 3^2 * 7^2;

a(11) = 525 = 3 * 5^2 * 7;

a(12) = 539 = 7^2 * 11.

MATHEMATICA

pf4Q[n_]:=Module[{pfs=Transpose[FactorInteger[n]][[1]]}, Max[pfs]- Min[pfs]==4]; Select[Range[11000], pf4Q] (* Harvey P. Dale, Sep 24 2011 *)

PROG

(Haskell)

a195106 n = a195106_list !! (n-1)

a195106_list = filter (\x -> a006530 x - a020639 x == 4) [1, 3..]

CROSSREFS

Cf. A195118, A143206; A143203 is a subsequence.

Sequence in context: A081302 A058100 A219856 * A143203 A082060 A025525

Adjacent sequences:  A195103 A195104 A195105 * A195107 A195108 A195109

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Sep 13 2011

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified June 25 19:53 EDT 2017. Contains 288729 sequences.