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Search: id:A085866
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| A085866 |
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a(1) = 3, a(n+1) = a(n)*{phi(a(n))}, where phi(n) is the Euler's coprime function. |
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2
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| 3, 6, 12, 48, 768, 196608, 12884901888, 55340232221128654848, 1020847100762815390390123822295304634368, 347376267711948586270712955026063723559809953996921692118372752023739388919808
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OFFSET
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1,1
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COMMENT
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(1). a(1) = 1, a(n+1) = a(n) + phi(a(n)) gives A074693. (2). for n>1, a(n)/3 is 2^(2^(n-2). And this sequence is; 2,4,16,256,... this is nothing but phi(a(n-1)).
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FORMULA
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a(n) = 3*2^(2^(n-2)).
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EXAMPLE
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a(3) = 12 and phi(12)= 4, hence a(4) = 12*4 = 48.
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PROGRAM
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(PARI) for(n=1, 11, if(n==1, a=3, a*=eulerphi(a)); print(a); )
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CROSSREFS
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Cf. A074693, A085864, A085865.
Cf. A000215.
Adjacent sequences: A085863 A085864 A085865 this_sequence A085867 A085868 A085869
Sequence in context: A136121 A023369 A129380 this_sequence A139416 A013563 A009788
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Jul 06 2003
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EXTENSIONS
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More terms from Ray Chandler (rayjchandler(AT)sbcglobal.net), Jul 16 2003
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