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 A068813 Primes with a 3 followed by 1's. 1
 31, 311, 311111, 31111111111, 311111111111, 31111111111111, 31111111111111111111111111111111111, 311111111111111111111111111111111111111111111111, 31111111111111111111111111111111111111111111111111111 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Makoto Kamada, Prime numbers of the form 311...11. H. C. Williams, Some primes with interesting digit patterns, Math. Comp. vol 32 no 144 (1978) pp 1306-1310, Table 2, r=3. EXAMPLE Digit 3 followed by rep-units of length 1,2,5,10,11,13,34,47,52,77,88,... MATHEMATICA Select[Table[FromDigits[PadRight[{3}, n, 1]], {n, 2, 100}], PrimeQ] (* Harvey P. Dale, Nov 18 2012 *) PROG (PARI) for(n=1, 200, if(isprime(3*10^n+(10^(n)-1)/9)==1, print1(3*10^n+(10^(n)-1)/9, ", "))) CROSSREFS Cf. A002275, A056704. Sequence in context: A200913 A212235 A126552 * A221306 A142382 A137318 Adjacent sequences:  A068810 A068811 A068812 * A068814 A068815 A068816 KEYWORD nonn,base AUTHOR Amarnath Murthy, Mar 07 2002 EXTENSIONS More terms from Benoit Cloitre, Mar 09 2002 One additional term from Harvey P. Dale, Nov 18 2012 STATUS approved

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Last modified June 20 09:27 EDT 2019. Contains 324234 sequences. (Running on oeis4.)