#math trivia for #September15: #258 consists of three digits in an arithmetic progression. Which other numbers in the 200s do?

— Burt Kaliski Jr. (@modulomathy) September 16, 2013

The digits 2, 5 and 8 form an arithmetic progression because each successive pair has the same difference: 5-2 = 8-5 = 3. The answers consist of the numbers with digits

- 2 a b

where a-2 = b-a. Alternatively, we have a = 2+d and b = 2+2d where d is the difference between consecutive digits. It is clear that d must be between -1 and 3 so that a and b will be between 0 and 9. The answers are thus:

- 210
- 222
- 234
- 246