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 A101841 Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 61 for n > 0. 1
 0, 4, 70, 111, 114, 172, 262, 309, 357, 10498, 22924, 37956, 254194 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (340*10^n - 61)/9 is prime. Numbers n such that digit 3 followed by n >= 0 occurrences of digit 7 followed by digit 1 is prime. Numbers corresponding to terms <= 357 are certified primes. a(14) >= 4*10^5. - Jason H Parker, Jun 15 2019 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 377...771. FORMULA a(n) = A102976(n) - 1. [adapted by Georg Fischer, Jan 04 2021] EXAMPLE 377771 is prime, hence 4 is a term. MATHEMATICA Select[Range[0, 300], PrimeQ[(340*10^# - 61)/9] &] (* Robert Price, May 08 2015 *) PROG (PARI) a=31; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+61) (PARI) for(n=0, 1500, if(isprime((340*10^n-61)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A102976. Sequence in context: A065573 A308294 A278553 * A274873 A281654 A222309 Adjacent sequences:  A101838 A101839 A101840 * A101842 A101843 A101844 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004 EXTENSIONS a(10)-a(12) from Kamada data by Ray Chandler, May 01 2015 a(13) from Jason H Parker, Jun 15 2019 STATUS approved

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Last modified December 6 06:14 EST 2021. Contains 349563 sequences. (Running on oeis4.)