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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A213017 Largest possible number of digits in a base n right-truncatable semiprime. 2
0, 0, 0, 8, 22, 30, 31, 35, 38, 43, 48, 51 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,4

COMMENTS

Right-truncatable semiprimes are numbers, where the number itself and all numbers obtained by successively removing the rightmost digit are semiprimes. S. S. Gupta found the largest possible right-truncatable base 10 semiprime to be 95861957783594714393831931415189937897 (38 decimal digits). Digit counts for largest possible right-truncatable semiprimes in other bases, found by Hermann Jurksch, are given in this sequence.

LINKS

Table of n, a(n) for n=2..13.

Shyam Sunder Gupta, The largest right-truncatable semiprime, Prime Curios.

EXAMPLE

There are no right-truncatable semiprimes in bases 2,3 and 4 thus a(2)=a(3)=a(4)=0;

The examples give the smallest base n semiprimes of maximum digit count, found by H. Jurksch:

a(5)=8: 42143413

a(6)=22: 4223145115415551545111

a(7)=30: 644324264233631242462662622646

a(8)=31: 4267773725372537135533515117773

a(9)=35: 43741424882428682844851886888222774

a(10)=38: 93359393537779942973989331953313839313

a(11)=43: 4567476a2738a828994aa851a116aa886a95686a231

a(12)=48: 43a2971ba155719171a2b1b97777775b779a732b755572b7

a(13)=51: 9114448462c6c46b3c9937446466b43686a246686667324c6a2

CROSSREFS

Cf. A085733, A213018

Sequence in context: A236917 A064193 A301482 * A305515 A063301 A030999

Adjacent sequences:  A213014 A213015 A213016 * A213018 A213019 A213020

KEYWORD

nonn,base,hard,more

AUTHOR

Hugo Pfoertner, Jun 07 2012

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 22 18:05 EST 2019. Contains 320400 sequences. (Running on oeis4.)