A201253 Numbers k such that phi(k+1) = 5*phi(k).
11242770, 18673200, 77805000, 117138840, 122649450, 278023200, 393513120, 881879460, 2177410830, 2364390210, 3440848320, 3919303080, 5151045900, 5836032510, 7284273360, 8029787220, 8505803460, 12998545560, 13081794180, 13759304790, 14031484740, 14104654410
Offset: 1
Keywords
Links
- Giovanni Resta, Table of n, a(n) for n = 1..92 (terms < 10^12)
Programs
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PARI
isok(k) = eulerphi(k+1) == 5*eulerphi(k); \\ Michel Marcus, Aug 10 2025
Extensions
a(9)-a(22) from Donovan Johnson, Nov 29 2011