A039780 Numbers k such that phi(k) is equal to A008473(k-1).

5, 25, 1176, 1625, 7385, 18633, 21726, 30276, 32923, 36905, 46025, 50809, 55449, 60726, 89257, 102425, 151657, 185745, 278226, 289961, 301017, 319145, 373176, 394121, 459513, 779817, 815676, 827926, 1053019, 1055719, 1170153, 1399123, 1657865, 1663209, 1667326

Offset: 1

Author

Olivier Gérard

Keywords

• nonn

Examples

			phi(1176)=336, 1175=5^2*47^1, (5+2)*(47+1)=336.
		

Crossrefs

Cf. A000010, A008473.

Cf. A039779, A039781.

Programs

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) = (k>1) && (eulerphi(k) == b(k-1)); \\ Michel Marcus, Feb 25 2021

Extensions

Title corrected and more terms from Sean A. Irvine, Feb 24 2021