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
Robert Israel, Table of n, a(n) for n = 1..1000
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
KEYWORD
nonn
AUTHOR
Washington Bomfim, Jan 24 2012
STATUS
approved