4 Positive Integers in Arithmetic Sequence which have Same Euler Phi Value/Mistake

Source Work

1986: David Wells: Curious and Interesting Numbers:

The Dictionary

$72$

1997: David Wells: Curious and Interesting Numbers (2nd ed.):

The Dictionary

$72$

Mistake

$\map \phi {72} = \map \phi {78} = \map \phi {84} = \map \phi {90} = 24$. This is the smallest set of four numbers in arithmetical progression whose $\phi$ values are equal. The next two $4$-term arithmetical progressions with equal $\phi$ values start at $216$ and $76,236$ and each has a common difference, $6$.

Correction

The last one of those should say $76,326$.

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $72$
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $72$