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 A082788 Numbers k such that the product of Euler phi of the 2 consecutive integers {k,k+1} is a 4th power: if sqrt(sqrt(phi(k)*phi(k+1))) is integer, then k is here. 4
 1, 259, 1260, 2071, 2834, 7574, 7749, 9252, 12800, 18720, 28236, 30039, 32724, 42120, 45395, 45877, 68124, 102656, 135813, 246543, 264440, 341288, 389455, 423163, 480624, 523775, 936471, 937248, 1055954, 1182104, 1295749, 1333626, 1366632, 1379196, 1458270, 1483118 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Amiram Eldar, Table of n, a(n) for n = 1..300 (terms 1..40 from Vincenzo Librandi) EXAMPLE k = 937248: phi(k) = 288000, phi(k+1) = 933120, 288000*933120 = 268738560000 = 720^4, so 937248 is here. MATHEMATICA f[x_] := EulerPhi[x]; Do[s=Sqrt[Sqrt[f[n+1]*f[n]]]; If[IntegerQ[s], Print[n]], {n, 1, 1000000}] PROG (PARI) isok(n) = ispower(eulerphi(n)*eulerphi(n+1), 4); \\ Michel Marcus, Jun 15 2017 CROSSREFS Sequence in context: A207060 A037987 A185673 * A043376 A038480 A309763 Adjacent sequences: A082785 A082786 A082787 * A082789 A082790 A082791 KEYWORD nonn AUTHOR Labos Elemer, May 21 2003 EXTENSIONS a(29)-a(36) from Vincenzo Librandi, Jun 15 2017 STATUS approved

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Last modified October 3 06:44 EDT 2023. Contains 365842 sequences. (Running on oeis4.)