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 A058214 Sum of solutions of phi(x) = 2^n. 4
 3, 13, 35, 105, 231, 581, 1315, 3225, 6711, 15221, 32755, 74505, 154407, 339397, 718115, 1589145, 3243831, 6946421, 14482675, 31259145, 63894567, 135588037, 281203235, 601400985, 1219907127, 2557715317, 5267017715, 11123540745, 22600784679, 47205887429 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS If there are only five Fermat primes, then a(n) = 2^(n-30) * 99852066765 for n > 31. - T. D. Noe, Jun 21 2012 LINKS T. D. Noe, Table of n, a(n) for n = 0..100 EXAMPLE For n=6, 2^n=64; the solutions of phi(x)=64 are {85,128,136,160,170,192,204,240}, whose sum is a(6)=1315. MATHEMATICA 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]]; Table[Plus@@phiinv[2^n], {n, 0, 30}] (* 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 *) CROSSREFS Cf. A000010, A001317, A003401, A004729, A019434, A045544, A047999, A053576, A054432, A058213, A058215. Sequence in context: A281868 A137976 A095661 * A108480 A322187 A146741 Adjacent sequences:  A058211 A058212 A058213 * A058215 A058216 A058217 KEYWORD nonn AUTHOR Labos Elemer, Nov 30 2000 EXTENSIONS Edited by Dean Hickerson, Jan 25 2002 a(28)-a(29) from Donovan Johnson, Oct 22 2011 STATUS approved

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Last modified September 26 17:30 EDT 2021. Contains 347670 sequences. (Running on oeis4.)