This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A056246 Indices of primes in sequence defined by A(0) = 11, A(n) = 10*A(n-1) + 41 for n > 0. 2
 0, 1, 3, 19, 31, 399, 561, 7015, 37683 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Numbers n such that (140*10^n - 41)/9 is a prime. Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 1 is a prime. Numbers corresponding to terms <= 561 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 - 151. Makoto Kamada, Prime numbers of the form 155...551. FORMULA a(n) = A082699(n-1) - 2 for n > 1. EXAMPLE 151 is a prime, hence 1 is a term. MATHEMATICA Select[Range[0, 2000], PrimeQ[(140 10^# - 41) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *) PROG (PARI) a=11; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+41) (PARI) for(n=0, 1500, if(isprime((140*10^n-41)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A068646, A082699. Sequence in context: A269414 A162307 A128069 * A061427 A069516 A098856 Adjacent sequences:  A056243 A056244 A056245 * A056247 A056248 A056249 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), 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 and updated 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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 17 01:41 EDT 2018. Contains 312693 sequences. (Running on oeis4.)