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Search: id:A099071
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| A099071 |
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Composite numbers n such that the concatenation of all nonprime natural numbers up to n in decreasing order is prime. |
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+0
4
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OFFSET
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1,1
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COMMENT
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The terms of this sequence are composite terms of the sequence A099070 with same order. Next term is greater than 6000 and the prime corresponding to the next term has more than 20000 digits. Number of digits of primes corresponding to the six known terms of the sequence are respectively 2,3,4,5,29 & 5010.
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LINKS
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C. Rivera, Primes by Listing.
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EXAMPLE
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26 is in the sequence because 26 is composite; nonprimes
up to 26 are 1,4,6,8,9,10,12,14,15,16,18,20,21,22,24,25,26
and 26252422212018161514121098641 is prime.
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MATHEMATICA
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Do[If[ !PrimeQ[n]&&PrimeQ[(v={}; Do[If[ !PrimeQ[n+1-j], v=Join[v, IntegerDigits[n+1-j]]], {j, n}]; FromDigits[v])], Print[n]], {n, 6013}]
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CROSSREFS
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Cf. A099070, A100003, A046284.
Sequence in context: A078337 A046351 A066307 this_sequence A073866 A001744 A113624
Adjacent sequences: A099068 A099069 A099070 this_sequence A099072 A099073 A099074
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KEYWORD
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base,more,nonn,nice
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AUTHOR
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Farideh Firoozbakht (f.firoozbakht(AT)math.ui.ac.ir), Nov 06 2004
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