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A185201
10^n - second largest prime less than 10^n.
1
5, 11, 9, 33, 11, 21, 27, 29, 71, 57, 53, 39, 137, 29, 53, 83, 23, 33, 57, 27, 113, 71, 53, 303, 321, 249, 107, 261, 53, 17, 81, 119, 47, 513, 237, 179, 123, 123, 173, 27, 203, 137, 119, 77, 119, 147, 83, 47, 183, 161, 333, 339, 611, 579
OFFSET
1,1
REFERENCES
D. E. Knuth, The Art of Computer Programming, Second Edition, Vol. 2, Seminumerical Algorithms, Chapter 4.5.4 Factoring into Primes, Table 1, Page 390, Addison-Wesley, Reading, MA, 1981.
LINKS
FORMULA
a(n) = 10^n - precprime(precprime(10^n)-1)
EXAMPLE
a(1) = 5 because precprime(10) = 7, and precprime(6) = 5.
From M. F. Hasler, Jul 19 2024: (Start)
Further examples: (where pp = prevprime = A151799)
n | pp(pp(10^n)) | a(n)
----+-----------------+------
1 | 5 | 5
2 | 89 | 11
3 | 991 | 9
4 | 9967 | 33
5 | 99989 | 11
6 | 999979 | 21
7 | 9999973 | 27
8 | 99999971 | 29
9 | 999999929 | 71
10 | 9999999943 | 57
11 | 99999999947 | 53
12 | 999999999961 | 39
13 | 9999999999863 | 137
14 | 99999999999971 | 29
15 | 999999999999947 | 53
(End)
MAPLE
seq(10^n - prevprime(prevprime(10^n)), n=1..100); # Robert Israel, May 28 2017
MATHEMATICA
Table[10^n - NextPrime[10^n, -2], {n, 1, 50}] (* G. C. Greubel, Jun 24 2017 *)
PROG
(PARI) apply( {A185201(n)=10^n-precprime(precprime(10^n)-1)}, [1..66]) \\ M. F. Hasler, Jul 19 2024
CROSSREFS
Cf. A033874.
Cf. A003618 (largest prime < 10^n), A151799 (prevprime function).
Sequence in context: A356480 A075261 A254766 * A112956 A258995 A335554
KEYWORD
nonn
AUTHOR
Washington Bomfim, Jan 24 2012
STATUS
approved