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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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FORMULA
| 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
| 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
| 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
| (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
| Cf. A000010, A051953, A055458, A063500, A054987.
Sequence in context: A065218 A187678 A124509 * A090765 A199910 A160728
Adjacent sequences: A063101 A063102 A063103 * A063105 A063106 A063107
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Aug 08 2001
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 03 2001.
a(29)-a(35) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Aug 18 2011
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