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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.
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
Sequence in context: A260227 A260226 A101149 * A213052 A355016 A260223
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 March 29 06:34 EDT 2024. Contains 371265 sequences. (Running on oeis4.)