I Stared At This For Ages:

[vetuste_ennemi]

You have a go.

Find the number that doesn't belong in the series below.

331, 482, 551, 263, 383, 362, 284

Difficulty Level: Medium
a) 263
b) 383
c) 331
d) 551
e) 284

[vetuste_ennemi]

Clue: I think I might have found this easier without the multiple choice.

[fiction-factory]

383

[vetuste_ennemi]

You got there a damn sight faster than I did, FF.

[johnny.5]

383

[vetuste_ennemi]

You beat me too, Johnny.

[vetuste_ennemi]

Do either of you agree with my comment about the multiple choice?

[Cloverjo]

Why, please?

[fiction-factory]

To me it stands out on both lists but I'm not sure why they list include only 5 of the 7 as options

[angie55]

multiply first number by third number to get second number.

[sanmac]

The only reason I can think of is that 383 has the same first and last digits.

[Cloverjo]

Thanks, Angie.

[sanmac]

It seems that I got it right but for the wrong reason:)

[vetuste_ennemi]

Yes, the middle digit is the product of the outer two.

I'd noticed of each of the two numbers not in the "choose from" group had a reverse entry in the full list.

[sanmac]

383, a palindromic number:)