The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

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