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 A102008 Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 81 for n > 0. 1
 0, 1, 2, 3, 8, 17, 21, 44, 48, 55, 68, 145, 201, 271, 2729, 2840, 4561, 31809, 43185, 48108, 92690 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Numbers n such that 10*10^n + 9 is prime. Numbers n such that digit 1 followed by n >= 0 occurrences of digit 0 followed by digit 9 is prime. Numbers corresponding to terms <= 271 are certified primes. a(22) > 2*10^5. - Robert Price, Oct 11 2015 REFERENCES Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. LINKS Table of n, a(n) for n=1..21. Makoto Kamada, Prime numbers of the form 100...009. FORMULA a(n) = A088275(n) - 1. EXAMPLE 1009 is prime, hence 2 is a term. MATHEMATICA Select[Range[0, 200000], PrimeQ[10*10^# + 9] &] (* Robert Price, Oct 11 2015 *) PROG (PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-81) (PARI) for(n=0, 1500, if(isprime(10*10^n + 9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A088275. Sequence in context: A277346 A005648 A113947 * A200083 A210701 A158921 Adjacent sequences: A102005 A102006 A102007 * A102009 A102010 A102011 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004 EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 a(21) from Kamada data by Ray Chandler, May 01 2015 STATUS approved

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Last modified December 2 02:40 EST 2023. Contains 367505 sequences. (Running on oeis4.)