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 A101952 Indices of primes in sequence defined by A(0) = 29, A(n) = 10*A(n-1) - 81 for n > 0. 1
 0, 4, 24, 454, 760, 9204, 13560, 15954, 26668, 113940 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that 20*10^n + 9 is prime. Numbers n such that digit 2 followed by n >= 0 occurrences of digit 0 followed by digit 9 is prime. Numbers corresponding to terms <= 760 are certified primes. a(11) > 2*10^5. - Robert Price, Jun 06 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 200...009. FORMULA a(n) = A101392(n-1) - 1. - Robert Price, Nov 25 2014 EXAMPLE 200009 is prime, hence 4 is a term. MATHEMATICA Select[Range[0, 300], PrimeQ[20*10^# + 9] &] (* Robert Price, Jun 06 2015 *) PROG (PARI) a=29; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-81) (PARI) for(n=0, 1500, if(isprime(20*10^n+9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A101392. Sequence in context: A296398 A166947 A103624 * A009535 A139096 A111425 Adjacent sequences:  A101949 A101950 A101951 * A101953 A101954 A101955 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004 EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 a(9)-a(10) derived from A101392 by Robert Price, Nov 25 2014 STATUS approved

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Last modified November 16 17:25 EST 2018. Contains 317275 sequences. (Running on oeis4.)