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Search: id:A077780
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| A077780 |
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Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)/9+3*10^[ a(n)/2 ]. |
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+0
2
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OFFSET
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1,1
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COMMENT
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Prime versus probable prime status and proofs are given in the author's table.
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REFERENCES
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C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
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LINKS
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Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)
Makoto Kamada, Factorizations of 11...11411...11
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FORMULA
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a(n) = 2*A107124(n)+1.
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EXAMPLE
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a(n)=7 -> (10^7-1)/9+3*10^3 = 1114111.
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MATHEMATICA
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Do[ If[ PrimeQ[(10^n + 27*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 3100, 2}] (from Robert G. Wilson v (rgwv(at)rgwv.com), Dec 16 2005)
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CROSSREFS
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Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A114633-A114647.
Sequence in context: A082714 A106112 A108200 this_sequence A130189 A073624 A025546
Adjacent sequences: A077777 A077778 A077779 this_sequence A077781 A077782 A077783
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KEYWORD
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nonn,base
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AUTHOR
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Patrick De Geest (pdg(AT)worldofnumbers.com), Nov 16 2002.
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