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Search: id:A101959
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| A101959 |
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Indices of primes in sequence defined by A(0) = 27, A(n) = 10*A(n-1) - 23 for n > 0. |
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+0
1
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| 2, 8, 14, 20, 26, 86, 179, 1940, 3959, 4994, 8576
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Numbers n such that (220*10^n + 23)/9 is prime.
Numbers n such that digit 2 followed by n >= 0 occurrences of digit 4 followed by digit 7 is prime.
Numbers corresponding to terms <= 179 are certified primes.
With alternating signs, expansion of cosh(atan(x)).
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REFERENCES
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Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
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LINKS
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Makoto Kamada, Factorizations of near-repdigit numbers.
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EXAMPLE
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2447 is prime, hence 2 is a term.
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PROGRAM
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(PARI) a=27; for(n=0, 2000, if(isprime(a), print1(n, ", ")); a=10*a-23)
(PARI) for(n=0, 2000, if(isprime((220*10^n+23)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275.
a(n) = A102954(n) - 1.
Sequence in context: A117104 A082933 A016933 this_sequence A133229 A046940 A046939
Adjacent sequences: A101956 A101957 A101958 this_sequence A101960 A101961 A101962
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KEYWORD
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nonn,hard,more
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AUTHOR
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Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004
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EXTENSIONS
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More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
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