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 A101722 Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 61 for n > 0. 1
 2, 2042, 5966, 39854 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that (380*10^n + 61)/9 is prime. Numbers n such that digit 4 followed by n >= 0 occurrences of digit 2 followed by digit 9 is prime. Some of the larger entries may only correspond to probable primes. Certified primality of number corresponding to term 2042 using Primo. - Ryan Propper, Jun 23 2005 a(5) > 10^5. - Robert Price, May 08 2015 REFERENCES Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. LINKS Makoto Kamada, Prime numbers of the form 422...229. FORMULA a(n) = A102987(n+1) - 1. EXAMPLE 4229 is prime, hence 2 is a term. MATHEMATICA Select[Range[0, 3000], PrimeQ[(380*10^# + 61)/9] &] (* Robert Price, May 08 2015 *) PROG (PARI) a=49; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-61) (PARI) for(n=0, 1500, if(isprime((380*10^n+61)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A102987. Sequence in context: A124361 A166339 A024034 * A004908 A275002 A004813 Adjacent sequences:  A101719 A101720 A101721 * A101723 A101724 A101725 KEYWORD nonn,bref,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004 EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007 a(4) from Kamada link by Ray Chandler, Apr 24 2015 STATUS approved

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Last modified June 28 01:48 EDT 2022. Contains 354903 sequences. (Running on oeis4.)