The On-Line Encyclopedia of Integer Sequences (OEIS)

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A110607

Numbers n whose base 9 representations, interpreted as base 10 integers, are semiprimes.
(history; published version)

#10 by Ray Chandler at Sat Oct 12 11:59:46 EDT 2019

STATUS

editing

approved

#9 by Ray Chandler at Sat Oct 12 11:59:43 EDT 2019

MATHEMATICA

Select[Range[181], Plus @@ Last /@ FactorInteger[FromDigits[IntegerDigits[ #, 9]]] == 2 &] (* _Ray Chandler_, Aug 05 2005 *)

STATUS

approved

editing

#8 by Harvey P. Dale at Sun Dec 02 19:15:13 EST 2018

STATUS

editing

approved

#7 by Harvey P. Dale at Sun Dec 02 19:15:10 EST 2018

LINKS

Harvey P. Dale, <a href="/A110607/b110607.txt">Table of n, a(n) for n = 1..1000</a>

MATHEMATICA

Select[Range[200], PrimeOmega[FromDigits[IntegerDigits[#, 9]]]==2&] (* Harvey P. Dale, Dec 02 2018 *)

STATUS

approved

editing

#6 by Russ Cox at Fri Mar 30 18:40:29 EDT 2012

AUTHOR

_Jonathan Vos Post (jvospost3(AT)gmail.com), _, Jul 30 2005

Discussion

Fri Mar 30

18:40

OEIS Server: https://oeis.org/edit/global/228

#5 by Russ Cox at Fri Mar 30 17:29:49 EDT 2012

EXTENSIONS

Extended by _Ray Chandler (rayjchandler(AT)sbcglobal.net), _, Aug 05 2005

Discussion

Fri Mar 30

17:29

OEIS Server: https://oeis.org/edit/global/154

#4 by N. J. A. Sloane at Fri Feb 27 03:00:00 EST 2009

EXAMPLE

a(3) = 9 because 9 (base 9) = 10, and 10 (base 10) = 2 * 5.

a(4) = 13 because 13 (base 9) = 14, and 14 (base 10) = 2 * 7.

a(5) = 14 because 14 (base 9) = 15, and 15 (base 10) = 3 * 5.

KEYWORD

base,easy,nonn,new

#3 by N. J. A. Sloane at Fri Jan 09 03:00:00 EST 2009

KEYWORD

base,easy,nonn,new

AUTHOR

Jonathan Vos Post (jvospost2jvospost3(AT)yahoogmail.com), Jul 30 2005

#2 by N. J. A. Sloane at Fri Jan 12 03:00:00 EST 2007

KEYWORD

base,easy,nonn,new

EXTENSIONS

Extended by Ray Chandler (RayChandlerrayjchandler(AT)alumni.tcusbcglobal.edunet), Aug 05 2005

#1 by N. J. A. Sloane at Wed Sep 21 03:00:00 EDT 2005

NAME

Numbers n whose base 9 representations, interpreted as base 10 integers, are semiprimes.

DATA

4, 6, 9, 13, 14, 19, 20, 23, 24, 30, 31, 32, 35, 42, 46, 50, 52, 53, 56, 59, 67, 70, 74, 77, 78, 79, 87, 91, 95, 98, 100, 101, 102, 111, 112, 118, 119, 120, 122, 123, 131, 134, 136, 141, 151, 152, 156, 158, 160, 163, 164, 165, 167, 168, 174, 175, 176, 178, 179, 181

OFFSET

1,1

COMMENTS

A108873 is the equivalent using base 3. A110602 is the equivalent using base 4. A110603 is the equivalent using base 5. A110604 is the equivalent using base 6. A110605 is the equivalent using base 7. A110606 is the equivalent using base 8.

EXAMPLE

a(1) = 4 because 4 (base 9) = 4 (base 10) = 2 * 2, a semiprime (A001358).

a(2) = 6 because 6 (base 9) = 6 (base 10) = 2 * 3.

a(3) = 9 because 9 (base 9) = 10, and 10 (base 10) = 2 * 5.

a(4) = 13 because 13 (base 9) = 14, and 14 (base 10) = 2 * 7.

a(5) = 14 because 14 (base 9) = 15, and 15 (base 10) = 3 * 5.

MATHEMATICA

Select[Range[181], Plus @@ Last /@ FactorInteger[FromDigits[IntegerDigits[ #, 9]]] == 2 &] (*Chandler*)

CROSSREFS

Cf. A001358, A007095, A108873, A110602, A110603, A110604, A110605, A110607.

KEYWORD

base,easy,nonn

AUTHOR

Jonathan Vos Post (jvospost2(AT)yahoo.com), Jul 30 2005

EXTENSIONS

Extended by Ray Chandler (RayChandler(AT)alumni.tcu.edu), Aug 05 2005

STATUS

approved