A039781 Numbers k such that phi(k) is equal to A008473(k+1).
55, 174, 183, 341, 407, 1274, 5424, 6887, 18903, 22167, 27559, 53847, 66711, 68237, 77957, 78155, 91524, 132791, 133574, 138471, 149435, 191575, 220759, 274224, 339024, 413424, 432233, 493724, 505735, 543221, 684167, 694823, 703824, 711774, 747175, 883463
Offset: 1
Keywords
Examples
phi(174)=56, 175=5^2*7^1, (5+2)*(7+1)=56.
Programs
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PARI
b(n)=my(f = factor(n)); for (k=1, #f~, f[k, 1] = f[k, 1] + f[k, 2]; f[k, 2] = 1; ); factorback(f); \\ A008473 isok(k) = eulerphi(k) == b(k+1); \\ Michel Marcus, Feb 25 2021
Extensions
Title corrected and more terms from Sean A. Irvine, Feb 24 2021