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 A101006 Indices of primes in sequence defined by A(0) = 91, A(n) = 10*A(n-1) + 31 for n > 0. 1
 1, 3, 7, 2959, 4570, 5200, 17863, 21921, 89374 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (850*10^n - 31)/9 is prime. Numbers n such that digit 9 followed by n >= 0 occurrences of digit 4 followed by digit 1 is prime. Some of the larger entries may only correspond to probable primes. a(10) > 10^5. - Robert Price, Nov 07 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 944...441. FORMULA a(n) = A103097(n) - 1. EXAMPLE 944444441 is prime, hence 7 is a term. MATHEMATICA Select[Range[0, 100000], PrimeQ[(850*10^# - 31)/9] &] (* Robert Price, Nov 07 2015 *) PROG (PARI) a=91; for(n=0, 3000, if(isprime(a), print1(n, ", ")); a=10*a+31) (PARI) for(n=0, 3000, if(isprime((850*10^n-31)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A103097. Sequence in context: A175986 A296351 A349007 * A306632 A083461 A137029 Adjacent sequences: A101003 A101004 A101005 * A101007 A101008 A101009 KEYWORD nonn,hard,more,less AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004 EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 a(7)-a(8) from Kamada data by Ray Chandler, Apr 28 2015 a(9) from Robert Price, Nov 07 2015 STATUS approved

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Last modified March 23 09:28 EDT 2023. Contains 361443 sequences. (Running on oeis4.)