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A006511
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Largest inverse of totient function (A000010): a(n) is the largest x such that phi(x)=m, where m=A002202(n) is the n-th number in the range of phi.
(Formerly M1580)
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13
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2, 6, 12, 18, 30, 22, 42, 60, 54, 66, 46, 90, 58, 62, 120, 126, 150, 98, 138, 94, 210, 106, 162, 174, 118, 198, 240, 134, 142, 270, 158, 330, 166, 294, 276, 282, 420, 250, 206, 318, 214, 378, 242, 348, 354, 462, 254, 510, 262, 414, 274, 278, 426, 630, 298, 302
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OFFSET
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1,1
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COMMENTS
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Always even, as phi(2n)=phi(n) when n is odd. - Alain Jacques (thegentleway(AT)bigpond.com), Jun 15 2006
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REFERENCES
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J. W. L. Glaisher, Number-Divisor Tables. British Assoc. Math. Tables, Vol. 8, Camb. Univ. Press, 1940, p. 64.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..10000
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FORMULA
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a(n) = A057635(A002202(n)). - T. D. Noe
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MATHEMATICA
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phiinv[n_, pl_] := Module[{i, p, e, pe, val}, If[pl=={}, Return[If[n==1, {1}, {}]]]; val={}; p=Last[pl]; For[e=0; pe=1, e==0||Mod[n, (p-1)pe/p]==0, e++; pe*=p, val=Join[val, pe*phiinv[If[e==0, n, n*p/pe/(p-1)], Drop[pl, -1]]]]; Sort[val]]; phiinv[n_] := phiinv[n, Select[1+Divisors[n], PrimeQ]]; Last/@Select[phiinv/@Range[1, 200], #!={}&] (* phiinv[n, pl] = list of x with phi(x)=n and all prime divisors of x in list pl. phiinv[n] = list of x with phi(x)=n *)
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CROSSREFS
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Cf. A000010, A002202, A002181.
For records see A036913, A132154, A036912.
Sequence in context: A108585 A193764 A159793 * A113274 A181660 A036913
Adjacent sequences: A006508 A006509 A006510 * A006512 A006513 A006514
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane.
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STATUS
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approved
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