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Search: id:A101137
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| A101137 |
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Indices of primes in sequence defined by A(0) = 71, A(n) = 10*A(n-1) + 21 for n > 0. |
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+0
1
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| 0, 2, 3, 4, 5, 8, 11, 30, 58, 68, 73, 286, 488, 591, 633, 1088, 1606, 3140, 5961, 6266, 9677, 11430, 12926
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Numbers n such that (660*10^n - 21)/9 is prime.
Numbers n such that digit 7 followed by n >= 0 occurrences of digit 3 followed by digit 1 is prime.
Numbers corresponding to terms <= 633 are certified primes.
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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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7333331 is prime, hence 5 is a term.
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PROGRAM
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(PARI) a=71; for(n=0, 1200, if(isprime(a), print1(n, ", ")); a=10*a+21)
(PARI) for(n=0, 1200, if(isprime((660*10^n-21)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275.
a(n) = A103055(n) - 1.
Sequence in context: A078762 A103262 A135318 this_sequence A053021 A122700 A048486
Adjacent sequences: A101134 A101135 A101136 this_sequence A101138 A101139 A101140
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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 03 2004
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EXTENSIONS
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More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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