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 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 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

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Last modified May 30 08:43 EDT 2020. Contains 334712 sequences. (Running on oeis4.)