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 A101069 Indices of primes in sequence defined by A(0) = 89, A(n) = 10*A(n-1) - 41 for n > 0. 1
 0, 3, 12, 36, 45, 105, 138, 468, 5694, 56280, 58669 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (760*10^n + 41)/9 is prime. Numbers n such that digit 8 followed by n >= 0 occurrences of digit 4 followed by digit 9 is prime. Numbers corresponding to terms <= 468 are certified primes. 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 844...449. FORMULA a(n) = A103082(n+1) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 EXAMPLE 84449 is prime, hence 3 is a term. MATHEMATICA Select[Range[0, 5700], PrimeQ[FromDigits[Join[PadRight[{8}, #+1, 4], {9}]]]&] (* Harvey P. Dale, Jan 23 2012 *) PROG (PARI) a=89; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-41) (PARI) for(n=0, 1000, if(isprime((760*10^n+41)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A103082. Sequence in context: A232899 A009787 A135190 * A225259 A334891 A242526 Adjacent sequences:  A101066 A101067 A101068 * A101070 A101071 A101072 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 30 2004 EXTENSIONS One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 a(10)-a(11) from Robert Price, Oct 18 2015 STATUS approved

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Last modified May 26 22:58 EDT 2020. Contains 334634 sequences. (Running on oeis4.)