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A108837 Primes of the form 5*10^n-7. 2
43, 4993, 49993, 499999993, 499999999999993, 49999999999999993, 4999999999999999999999993, 49999999999999999999999999999999999999999999999999999999999993 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Primes such that the leftmost digit is 4, the rightmost digit is 3, and all inner digits are 9.

LINKS

Table of n, a(n) for n=1..8.

Makoto Kamada, Prime numbers of the form 499...993.

FORMULA

a(n) = 5*10^A103002(n) - 7.

MATHEMATICA

Select[Table[FromDigits[Join[PadRight[{4}, n+1, 9], {3}]], {n, 0, 150}], PrimeQ] (* Harvey P. Dale, Feb 01 2012 *)

PROG

(PARI) n10np9(n, d) = { local(x, y, k); for(x=1, n, for(k=1, 8, y=10^(x+1)*k+(10^x-1)*10+k-1; if(isprime(y), print1(y", ")) ) ) }

(MAGMA)[a: n in [1..250]|IsPrime(a) where a is (5*10^n-7)] // Vincenzo Librandi, Dec 11 2010

(PARI) for(n=4, 99, if(ispseudoprime(t=10^n/2-7), print1(t", "))) \\ Charles R Greathouse IV, Feb 01 2012

CROSSREFS

Cf. A103002, A101739.

Sequence in context: A110704 A060485 A081795 * A091748 A208625 A147522

Adjacent sequences:  A108834 A108835 A108836 * A108838 A108839 A108840

KEYWORD

easy,nonn,base

AUTHOR

Cino Hilliard, Jul 11 2005

EXTENSIONS

Edited by Ray Chandler, Feb 03 2012

Comments amended by Harvey P. Dale, Feb 03 2012

STATUS

approved

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Last modified June 6 04:15 EDT 2020. Contains 334859 sequences. (Running on oeis4.)