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A153332 Numbers n such that (10^n-1)*150/99 + 1 is prime. 0
2, 14, 62, 88, 244, 582, 1790 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

These numbers are always even. If n is odd, then 10^n-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=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^ln-1)+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

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Last modified June 5 11:52 EDT 2020. Contains 334840 sequences. (Running on oeis4.)