A153333 Numbers k such that (10^k - 1)*160/99 + 1 is prime.

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.

Links

Table of n, a(n) for n=1..6.

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

Adjacent sequences: A153330 A153331 A153332 * A153334 A153335 A153336

Keyword

nonn,base,more

Author

Cino Hilliard, Dec 23 2008

Status

approved