A268126 - OEIS

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A268126

Numbers n such that phi(n) = 4*phi(n-1).

1261, 13651, 17557, 18721, 24511, 42121, 113611, 244531, 266071, 712081, 749911, 795691, 992251, 1080721, 1286731, 1458271, 1849471, 2271061, 2457691, 3295381, 3370771, 3414841, 3714751, 4061971, 4736491, 5314051, 5827081, 6566911, 6935083, 7303981, 7864081

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OFFSET

1,1

COMMENTS

See A266276(n) = the smallest numbers k such that phi(k) = n * phi(k-1) for n >=1: 2, 3, 7, 1261, 11242771, ...

LINKS

Table of n, a(n) for n=1..31.

FORMULA

a(n) = A172314(n) + 1. - Michel Marcus, Jan 27 2016

EXAMPLE

1261 is in the sequence because phi(1261) = 1152 = 4*phi(1260) = 4*288.

MATHEMATICA