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Search: id:A134039
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| A134039 |
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First prime divisor of odd composite Mersenne prime reversals. |
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+0
3
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OFFSET
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1,1
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COMMENT
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The UBASIC program below was used to find A(3)=683. Suggested by Puzzle 417, Carlos Rivera's The Prime Puzzles & Problems Connection (puzzle inspired by G. L. Honaker, Jr.'s Prime Curios)
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FORMULA
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Generate the sequence of Mersenne primes, reverse each, and test for primality. If the reversal is an odd composite, find the first prime divisor.
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EXAMPLE
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a(2) = 13 because the 6th Mersenne prime is 2^17-1 = 131071. Reversed this number is 170131, which is equal to 13*13087.
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PROGRAM
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UBASIC to find a(3)=683. 10 'primes using counters 20 N=727501488517303786137132964064381141071 30 A=3:S=sqrt(N):C="c" 40 B=N\A 50 if B*A=N then print B; A; N; "-"; :N=N+2:goto 30 60 A=A+2 70 if A<=sqrt(N) then 40 80 if N>2 then stop 81 C=C+1 90 print C; N; "-"; 100 N=N+2:goto 30
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CROSSREFS
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Cf. A134037 A134038.
Sequence in context: A087820 A023286 A146648 this_sequence A116522 A108056 A018562
Adjacent sequences: A134036 A134037 A134038 this_sequence A134040 A134041 A134042
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KEYWORD
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base,nonn
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AUTHOR
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Enoch Haga (Enokh(AT)comcast.net), Oct 02 2007
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