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 A056260 Indices of primes in sequence defined by A(0) = 77, A(n) = 10*A(n-1) - 3 for n > 0. Numbers n such that (690*10^n + 3)/9 is prime. 2
 3, 5, 53, 95, 453, 573, 3383, 11439, 12623, 19445, 35459, 81213, 95325 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that digit 7 followed by n >= 0 occurrences of digit 6 followed by digit 7 is prime. Numbers corresponding to terms <= 3383 are certified primes. REFERENCES Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. LINKS Patrick De Geest, PDP Reference Table - 767. Makoto Kamada, Prime numbers of the form 766...667. FORMULA a(n) = A082714(n) - 2. EXAMPLE 76667 is prime, hence 3 is a term. MATHEMATICA Select[Range[3500], PrimeQ[(690 10^# + 3) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *) PROG (PARI) a=77; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-3) (PARI) for(n=0, 1000, if(isprime((690*10^n+3)/9), print1(n, ", "))) (MAGMA) [n: n in [0..300] | IsPrime((690*10^n+3) div 9)]; // Vincenzo Librandi, Nov 03 2014 CROSSREFS Cf. A000533, A002275, A082714. Sequence in context: A260227 A260226 A101149 * A213052 A260223 A260225 Adjacent sequences:  A056257 A056258 A056259 * A056261 A056262 A056263 KEYWORD hard,nonn AUTHOR Robert G. Wilson v, Aug 18 2000 EXTENSIONS Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, Apr 29 2007, Jun 15 2007 a(7)-a(11) from Robert G. Wilson v, May 02 2007 Two more terms added from PDP Table, a link added and comments section updated by Patrick De Geest, Nov 02 2014 Edited by Ray Chandler, Nov 05 2014 STATUS approved

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Last modified February 17 12:14 EST 2020. Contains 331996 sequences. (Running on oeis4.)