A085733 Right-truncatable semiprimes.
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
Offset: 1
References
- Shyam Sunder Gupta, Truncatable semi-primes, Mathematical Spectrum 39:3 (2007), pp. 109-112.
Links
- Michael S. Branicky, Table of n, a(n) for n = 1..56076 (full sequence).
- I. O. Angell and H. J. Godwin, On truncatable primes, Math. Comput. 31:137, 265-267, 1977.
- G. L. Honaker, Jr., Prime Curios! 46613113151331733179
- Shyam Sunder Gupta, The largest right-truncatable semiprime. Prime Curios.
- Index entries for sequences related to truncatable primes
Programs
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Python
from sympy import factorint from itertools import islice def issemiprime(n): return sum(factorint(n).values()) == 2 def agen(): semis, digits = [4, 6, 9], "123456789" # can't end in 0 while len(semis) > 0: yield from semis cands = set(int(str(p)+d) for p in semis for d in digits) semis = sorted(c for c in cands if issemiprime(c)) print(list(islice(agen(), 50))) # Michael S. Branicky, Aug 04 2022
Extensions
More terms from Reinhard Zumkeller, Jul 22 2003
More terms from Hugo Pfoertner, Jul 22 2003
Comments