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 A101061 Indices of primes in sequence defined by A(0) = 81, A(n) = 10*A(n-1) + 11 for n > 0. 1
 1, 2, 4, 16, 46, 176, 8461, 36614 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (740*10^n - 11)/9 is prime. Numbers n such that digit 8 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime. Numbers corresponding to terms <= 176 are certified primes. a(9) > 10^5. - Robert Price, Oct 13 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 822...221. FORMULA a(n) = A103074(n+1) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 EXAMPLE 822221 is prime, hence 4 is a term. MATHEMATICA Select[Range[0, 100000], PrimeQ[(740*10^# - 11)/9] &] (* Robert Price, Oct 13 2015 *) PROG (PARI) a=81; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+11) (PARI) for(n=0, 1000, if(isprime((740*10^n-11)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A103074. Sequence in context: A133465 A110128 A148279 * A148280 A112638 A077162 Adjacent sequences:  A101058 A101059 A101060 * A101062 A101063 A101064 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 30 2004 EXTENSIONS 8461 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 a(8) from Erik Branger May 01 2013 by Ray Chandler, Apr 29 2015 STATUS approved

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Last modified December 4 10:44 EST 2021. Contains 349486 sequences. (Running on oeis4.)