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A124450
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Lesser of a pair of not necessarily distinct closest primes that add up to 10^n.
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5
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5, 47, 491, 4919, 49877, 499943, 4999913, 49999757, 499999931, 4999999937, 49999999811, 499999999769, 4999999998431, 49999999999619, 499999999999769, 4999999999998557, 49999999999998887, 499999999999999679
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OFFSET
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1,1
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COMMENTS
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a(n) is always an n digit number.
Note that if distinct primes are required, the only change is that a(1) = 3.
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LINKS
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FORMULA
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10^n - a(n) is prime.
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EXAMPLE
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10^1=5+5; 10^2=47+53; 10^3=491+509;
10^4=4919+5081; 10^5=49877=50123; 10^6=499943+500057;
10^7=4999913+5000087; 10^8=49999757+50000243;
10^9=499999931+500000069;
10^10=4999999937+5000000063}, etc.
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MATHEMATICA
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Table[ h =10^n/2; c=0; While[ PrimeQ[ h-c ]==False || PrimeQ[ h+c ]==False, c++ ]; h-c, {n, 1, 50} ] (from Hans Havermann, Nov 02 2006)
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CROSSREFS
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Cf. A065577 = number of Goldbach partitions of 10^n.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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