

A153332


Numbers n such that (10^n1)*150/99 + 1 is prime.


0




OFFSET

0,1


COMMENTS

These numbers are always even. If n is odd, then 10^n1 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=0..6.


EXAMPLE

For the first entry n=2 the formula produces the prime 151.


MATHEMATICA

2*Floor[IntegerLength[#]/2]&/@Select[Table[FromDigits[Join[{1}, PadRight[ {}, 2n, {5, 1}]]], {n, 1000}], PrimeQ] (* Harvey P. Dale, Jun 27 2012 *)


PROG

(PARI) /* n=number of values to test, r=repeat digits, eg., 14, 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^ln1)+1; if(ispseudoprime(y), print1(ln*x", ")))


CROSSREFS

Sequence in context: A174704 A058738 A095376 * A331822 A217154 A144657
Adjacent sequences: A153329 A153330 A153331 * A153333 A153334 A153335


KEYWORD

nonn,base


AUTHOR

Cino Hilliard, Dec 23 2008


EXTENSIONS

a(7) provided by Harvey P. Dale, Jun 27 2012


STATUS

approved



