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 A271633 Numbers k such that sigma(phi(k)) - phi(k) = phi(sigma(k)), where phi(k) is the Euler totient function of k and sigma(k) is the sum of the divisors of k. 1
 21, 350, 366, 532, 702, 1072, 5264, 7128, 23604, 24102, 30222, 30636, 32142, 32274, 34350, 47338, 70722, 78530, 113550, 137214, 197316, 235624, 292206, 357490, 367704, 398346, 406596, 453096, 453264, 464820, 479880, 485460, 504966, 509124, 512430, 519870, 539220 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Amiram Eldar, Table of n, a(n) for n = 1..215 (terms below 10^9) EXAMPLE sigma(phi(21)) - phi(21) = 28 - 12 = 16 = phi(sigma(21)). MAPLE with(numtheory): P:= proc(q) local n; for n from 1 to q do if sigma(phi(n))-phi(n)=phi(sigma(n)) then print(n); fi; od; end: P(10^6); MATHEMATICA Select[Range[10^6], DivisorSigma[1, #] - # &@ EulerPhi@ # == EulerPhi@ DivisorSigma[1, #] &] (* Michael De Vlieger, Apr 21 2016 *) PROG (PARI) isok(k) = my(x=eulerphi(k)); sigma(x) - x == eulerphi(sigma(k)); \\ Michel Marcus, Jul 13 2019 CROSSREFS Cf. A000010, A000203, A001065, A033632, A062401. Sequence in context: A299813 A299688 A300320 * A184289 A192093 A006105 Adjacent sequences: A271630 A271631 A271632 * A271634 A271635 A271636 KEYWORD nonn AUTHOR Paolo P. Lava, Apr 19 2016 STATUS approved

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Last modified October 3 13:14 EDT 2023. Contains 365862 sequences. (Running on oeis4.)