This site is supported by donations to The OEIS Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A056248 Indices of primes in sequence defined by A(0) = 11, A(n) = 10*A(n-1) + 61 for n > 0. 1
 0, 5, 47, 101, 191, 365, 1001, 20363, 37445, 56081 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (160*10^n - 61)/9 is prime. Numbers n such that digit 1 followed by n >= 0 occurrences of digit 7 followed by digit 1 is prime. Numbers corresponding to terms <= 1001 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 - 171. Makoto Kamada, Prime numbers of the form 177...771. FORMULA a(n) = A082701(n-1) - 2 for n > 1. EXAMPLE 1777771 is prime, hence 5 is a term. MATHEMATICA Flatten[Position[NestList[10#+61&, 11, 38000], _?PrimeQ]-1] (* Harvey P. Dale, Apr 17 2014 *) Select[Range[0, 2000], PrimeQ[(160 10^# - 61) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *) PROG (PARI) a=11; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+61) (PARI) for(n=0, 1500, if(isprime((160*10^n-61)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A082701. Sequence in context: A196160 A136088 A141890 * A126575 A229613 A277607 Adjacent sequences:  A056245 A056246 A056247 * A056249 A056250 A056251 KEYWORD nonn,hard,more,changed AUTHOR Robert G. Wilson v, Aug 18 2000 EXTENSIONS Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004 Edited by N. J. A. Sloane, Jun 15 2007 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 Added one more term from PDP table and a link. Updated comments section and a link, 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 | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified January 18 05:30 EST 2019. Contains 319269 sequences. (Running on oeis4.)