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Search: id:A063104
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| A063104 |
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a(0) = 0, a(n) = smallest composite x such that Phi[x + 2^n] = Phi[x] + 2^n; also Cototient[x + 2^n] = Cototient[x]. |
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1
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| 0, 6, 12, 24, 39, 84, 69, 75, 213, 1092, 249, 1131, 8736, 13413, 21201, 1275, 2193, 279552, 98337, 968727, 71085, 2783555, 646869, 3145959, 1805781, 5798435, 787605, 27962075, 2073033
(list; graph; listen)
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OFFSET
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0,2
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FORMULA
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a(n) = Min{x: A000010(n)+2^n = A000010(x+2^n)} = Min{x: A051953(x+2^n) = A051953(n)}
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EXAMPLE
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n=4, a(4)=39, Phi[39]+16=24+16=40=Phi[55]; a(14) = 21201, Phi(21201) + 2^14 = 13680 + 16384 = 30064 = Phi(37585).
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MATHEMATICA
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Do[k = 4; While[ PrimeQ[k] || EulerPhi[k + 2^n] != EulerPhi[k] + 2^n, k++ ]; Print[k], {n, 1, 28} ]
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PROGRAM
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(PARI) { n=0; f="b063104.txt"; write(f, "0 0"); for (n=1, 28, k=4; while (isprime(k) || eulerphi(k + 2^n) != eulerphi(k) + 2^n, k++); write(f, n, " ", k) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Aug 18 2009]
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CROSSREFS
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Cf. A000010, A051953, A055458, A063500, A054987.
Sequence in context: A140522 A065218 A124509 this_sequence A090765 A160728 A082505
Adjacent sequences: A063101 A063102 A063103 this_sequence A063105 A063106 A063107
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KEYWORD
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more,nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Aug 08 2001
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 03 2001.
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