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 A101958 Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) + 13 for n > 0. 1
 0, 3, 6, 11, 29, 93, 177, 195, 563, 1800, 3519, 3537, 8232, 35160, 37404, 42329, 70050, 90791 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (220*10^n - 13)/9 is prime. Numbers n such that digit 2 followed by n >= 0 occurrences of digit 4 followed by digit 3 is prime. Numbers corresponding to terms <= 563 are certified primes. With changed signs, expansion of sinh(atan(x)). Next term after 3537 is greater than 5000. - Ryan Propper, Jun 16 2005 a(19) > 10^5. - Robert Price, Mar 16 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..18. Makoto Kamada, Prime numbers of the form 244...443. Index entries for primes involving repunits. FORMULA a(n) = A102953(n) - 1. EXAMPLE 24443 is prime, hence 3 is a term. PROG (PARI) a=23; for(n=0, 2000, if(isprime(a), print1(n, ", ")); a=10*a+13) (PARI) for(n=0, 2000, if(isprime((220*10^n-13)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A102953. Sequence in context: A221182 A109781 A360888 * A153982 A119367 A079801 Adjacent sequences: A101955 A101956 A101957 * A101959 A101960 A101961 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004 EXTENSIONS 2 more terms from Ryan Propper, Jun 16 2005 8232 from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007 a(14)-a(18) derived from A102953 by Robert Price, Mar 16 2015 STATUS approved

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Last modified August 2 22:39 EDT 2024. Contains 374875 sequences. (Running on oeis4.)