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A153331 Numbers n such that (10^n-1)*140/99+1 is prime. 0
10, 276, 478, 582, 1630 (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. a(10) = 14141414141 which is prime. Also these numbers are palindromic.

LINKS

Table of n, a(n) for n=0..4.

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: A055055 A222998 A221526 * A290202 A203149 A117654

Adjacent sequences:  A153328 A153329 A153330 * A153332 A153333 A153334

KEYWORD

nonn,base

AUTHOR

Cino Hilliard, Dec 23 2008

STATUS

approved

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Last modified May 26 16:52 EDT 2020. Contains 334627 sequences. (Running on oeis4.)