

A085733


Righttruncatable semiprimes.


3



4, 6, 9, 46, 49, 62, 65, 69, 91, 93, 94, 95, 466, 469, 493, 497, 622, 623, 626, 629, 655, 694, 695, 697, 698, 699, 913, 914, 917, 933, 934, 939, 943, 949, 951, 955, 958, 959, 4661, 4666, 4667, 4694, 4699, 4934, 4939, 4971, 4979, 6227, 6233, 6238
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OFFSET

1,1


COMMENTS

Semiprimes in which repeatedly deleting the rightmost digit gives a semiprime at every step until a singledigit semiprime remains.
The sequence is finite. According to Shyam Sunder Gupta the number 95861957783594714393831931415189937897 is the largest righttruncatable semiprime.
The total number of righttruncatable semiprimes including the single digit semiprimes 4, 6 and 9 is 56076.  Shyam Sunder Gupta, Jan 13 2008


REFERENCES

Shyam Sunder Gupta, Truncatable semiprimes, Mathematical Spectrum 39:3 (2007), pp. 109112.


LINKS

Table of n, a(n) for n=1..50.
Index entries for sequences related to truncatable primes
I. O. Angell and H. J. Godwin, On truncatable primes, Math. Comput. 31:137, 265267, 1977.
G. L. Honaker, Jr., Prime Curios!
Shyam Sunder Gupta, The largest righttruncatable semiprime. Prime Curios.


CROSSREFS

Cf. A001358, A213019.
Sequence in context: A175459 A257652 A107665 * A242751 A107342 A086698
Adjacent sequences: A085730 A085731 A085732 * A085734 A085735 A085736


KEYWORD

base,fini,nonn


AUTHOR

G. L. Honaker, Jr., Jul 20 2003


EXTENSIONS

More terms from Reinhard Zumkeller, Jul 22 2003
More terms from Hugo Pfoertner, Jul 22 2003


STATUS

approved



