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Search: id:A095180
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| A095180 |
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Reverse digits of primes, append to sequence if result is a prime. |
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+0
2
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| 2, 3, 5, 7, 11, 31, 71, 13, 73, 17, 37, 97, 79, 101, 701, 311, 131, 941, 151, 751, 761, 971, 181, 191, 991, 113, 313, 733, 743, 353, 953, 373, 383, 983, 107, 907, 727, 337, 937, 347, 157, 757, 167, 967, 787, 797, 709, 919, 929, 739, 149, 359, 769, 179, 389, 199
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Conjecture: the Benford law limit is 2=Sum[N[Log[10, 1 + 1/d[[n]]]], {n, 1, Length[d]}]^2/(( #toralprimes/#totalPrimes)). At 50000 primes total it is 2.05931. - Roger L. Bagula and Gary W. Adamson (rlbagulatftn(AT)yahoo.com), Jul 02 2008
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REFERENCES
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Weisstein, Eric W. "Benford's Law." http://mathworld.wolfram.com/BenfordsLaw.html
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LINKS
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Roger L. Bagula and Gary W. Adamson (rlbagulatftn(AT)yahoo.com), Jul 02 2008, Table of n, a(n) for n = 1..206
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EXAMPLE
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The prime 107 in reverse is 701 which is prime.
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MATHEMATICA
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b = Flatten[Table[If[PrimeQ[Sum[IntegerDigits[Prime[n]][[i]]*10^(i - 1), {i, 1, Length[IntegerDigits[Prime[n]]]}]], Sum[IntegerDigits[Prime[n]][[i]]*10^(i - 1), {i, 1, Length[IntegerDigits[Prime[n]]]}], {}], {n, 1, 1000}]] - Roger L. Bagula and Gary W. Adamson (rlbagulatftn(AT)yahoo.com), Jul 02 2008
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PROGRAM
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(PARI) r(n) = forprime(x=1, n, y=eval(rev(x)); if(isprime(y), print1(y", "))) \ Get the reverse of the input string rev(str) = { local(tmp, j, s); tmp = Vec(Str(str)); s=""; forstep(j=length(tmp), 1, -1, s=concat(s, tmp[j])); return(s) }
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CROSSREFS
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Cf. A007500.
Sequence in context: A104154 A123214 A119834 this_sequence A101989 A098922 A004087
Adjacent sequences: A095177 A095178 A095179 this_sequence A095181 A095182 A095183
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KEYWORD
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base,easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Jun 21 2004
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