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A063104
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a(0) = 0, a(n) = smallest composite k such that phi(k + 2^n) = phi(k) + 2^n; also cototient(k + 2^n) = cototient(k).
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0
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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, 282181709, 1150329, 10380353, 516201, 150807855, 141521295, 860867981
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OFFSET
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0,2
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LINKS
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FORMULA
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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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PROG
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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) ) } \\ Harry J. Smith, Aug 18 2009
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CROSSREFS
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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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