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A153333
Numbers k such that (10^k - 1)*160/99 + 1 is prime.
0
6, 54, 108, 144, 228, 960
OFFSET
1,1
COMMENTS
These numbers are always even. If k is odd, then 10^k - 1 produces a number with an odd number of 9's which 99 does not divide. Also the numbers produced by this formula are palindromic.
EXAMPLE
For the first entry, k=6, the formula produces the prime 1616161.
PROG
(PARI) /* n=number of values to test, r=repeat digits, e.g., 16, 121, 177, 1234, etc. d = last digit appended to the end */
repr(n, r, d) = ln=length(Str(r)); for(x=0, n, y=(10^(ln*x)-1)*10*r/(10^ln-1)+1; if(ispseudoprime(y), print1(ln*x", ")))
CROSSREFS
Sequence in context: A145003 A248369 A097645 * A284858 A343982 A275039
KEYWORD
nonn,base,more
AUTHOR
Cino Hilliard, Dec 23 2008
STATUS
approved