The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A056264 Indices of primes in sequence defined by A(0) = 99, A(n) = 10*A(n-1) - 71 for n > 0. 1
 1, 245, 1139, 10393, 43879 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (820*10^n + 71)/9 is a prime. Numbers n such that digit 9 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime. Numbers corresponding to terms <= 1139 are certified primes. For number corresponding to 10393 and larger 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 - 919. Makoto Kamada, Prime numbers of the form 911...119. FORMULA a(n) = A082717(n) - 2. EXAMPLE 919 is prime, hence 1 is a term. MATHEMATICA Flatten[Position[NestList[10#-71&, 99, 1200], _?PrimeQ]]-1 (* Harvey P. Dale, May 02 2012 *) PROG (PARI) a=99; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-71) (PARI) for(n=0, 1500, if(isprime((820*10^n+71)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A082717. Sequence in context: A350421 A236887 A237161 * A154080 A259511 A023097 Adjacent sequences:  A056261 A056262 A056263 * A056265 A056266 A056267 KEYWORD nonn,hard AUTHOR Robert G. Wilson v, Aug 18 2000 EXTENSIONS Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004 Edited by N. J. A. Sloane, Jun 15 2007 One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 Edited comments section by Patrick De Geest, Nov 02 2014 Edited by Ray Chandler, Nov 04 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 17 00:01 EDT 2022. Contains 356180 sequences. (Running on oeis4.)