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 A056252 Indices of primes in sequence defined by A(0) = 33, A(n) = 10*A(n-1) - 7 for n > 0. 2
 5, 7, 893, 1523, 3035, 21155 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that (290*10^n + 7)/9 is prime. Numbers n such that the digit 3 followed by n >= 0 occurrences of the digit 2 followed by the digit 3 is prime. Numbers corresponding to terms <= 3035 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 - 323. Makoto Kamada, Prime numbers of the form 322...223. FORMULA a(n) = A082705(n) - 2. EXAMPLE 3222223 is prime, hence 5 is a term. MATHEMATICA Select[Range[0, 2000], PrimeQ[(290 10^# + 7) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *) PROG (PARI) a=33; for(n=0, 1600, if(isprime(a), print1(n, ", ")); a=10*a-7) (PARI) for(n=0, 1600, if(isprime((290*10^n+7)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A082705. Sequence in context: A114363 A083687 A101829 * A274774 A176599 A291687 Adjacent sequences:  A056249 A056250 A056251 * A056253 A056254 A056255 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 20 2004 Edited by N. J. A. Sloane, Apr 17 2007 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 Comments section updated and a link added by Patrick De Geest, Nov 02 2014 Edited by Ray Chandler, Nov 05 2014 STATUS approved

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Last modified January 18 04:47 EST 2019. Contains 319269 sequences. (Running on oeis4.)