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 A056263 Indices of primes in sequence defined by A(0) = 77, A(n) = 10*A(n-1) + 27 for n > 0. 1
 1, 3, 27, 155, 321, 351, 1211, 1283, 7983, 15191, 84771, 119929, 148859 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (720*10^n - 27)/9 is a prime. Numbers n such that digit 7 followed by n >= 0 occurrences of digit 9 followed by digit 7 is a prime. Numbers corresponding to terms <= 1283 are certified primes. For larger numbers see P. De Geest, PDP Reference Table. REFERENCES Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. LINKS Patrick De Geest, PDP Reference Table - 797. Makoto Kamada, Prime numbers of the form 799...997. FORMULA a(n) = A082716(n) - 2. EXAMPLE 797 is a prime, hence 1 is a term. PROG (PARI) a=77; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+27) (PARI) for(n=0, 1500, if(isprime((720*10^n-27)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A082716. Sequence in context: A174613 A127509 A108142 * A026093 A215711 A270956 Adjacent sequences:  A056260 A056261 A056262 * A056264 A056265 A056266 KEYWORD nonn,more AUTHOR Robert G. Wilson v, Aug 18 2000 EXTENSIONS Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004 Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, Jun 08 2007 Update from De Geest link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 a(11)=84771 from Ray Chandler, Jan 04 2011 a(12)=119929 from Ray Chandler, Apr 01 2011 a(13)=148859 from Ray Chandler, Apr 09 2011 Updated comments section by Patrick De Geest, Nov 02 2014 Edited by Ray Chandler, Nov 04 2014 STATUS approved

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Last modified September 18 23:30 EDT 2020. Contains 337175 sequences. (Running on oeis4.)