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 A030163 Solutions x of 2*uphi(x)=x, where uphi is the unitary phi function (A047994). 10
 2, 12, 168, 240, 14880, 65280, 4294901760, 7608944640, 1125874137169920, 18446744069414584320 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Tomohiro Yamada, An analog of perfect numbers involving the unitary totient function, arXiv:1806.00647 [math.NT], 2018. PROG (PARI) uphi(n) = my(f=factor(n)~); prod(i=1, #f, f[1, i]^f[2, i]-1); isok(n) = uphi(n) == n/2; \\ Michel Marcus, Feb 13 2018 (PARI) solve_uphi(N, D, limit) = {my(g, f, uphi, sol, p, n, pn, uphipn, tmp, ll); sol = []; g = gcd(N, D); N /= g; D /= g; if (D==1, if (N==1, sol = [1]); sol; , f = factor(D); uphi = prod(i=1, #f~, f[i, 1]^f[i, 2]-1); if (uphi(x <= limit), vecsort(sol, , 8)); } solve_uphi(1, 2, 10^20) \\ Michel Marcus, Jun 07 2018 CROSSREFS Cf. A047994. Sequence in context: A201007 A226058 A120958 * A255163 A052728 A052729 Adjacent sequences:  A030160 A030161 A030162 * A030164 A030165 A030166 KEYWORD nonn,more AUTHOR EXTENSIONS Corrected offset and keyword more by Michel Marcus, Feb 13 2018 STATUS approved

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Last modified September 16 23:53 EDT 2021. Contains 347477 sequences. (Running on oeis4.)