Question

Oftener

Answer 1

It is the comparative form of the adverb "often".

بیشتر، پرتکرارتر، مداوم تر، بیشتر از آن

http://www.yourdictionary.com/oftener

Answer 2

Oftener is an adverb not an adjective so it doesnot have a comparative form. It means more than once, frequently.

Comments

Adverbs, like adjectives, DO have comparative forms.

Look at these:

http://goo.gl/jyql6e

https://goo.gl/fI3ZPe

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In this case you are right, but I myself use more often since the adverbial of time "Often" is made of two syllables.

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According to all dictionaries, oftener and oftenest are correct too.

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"Oftener" and "More often" are both comparatives of the same adverb,often.They are both accepted as correct." More often" seems to be more common in the U.S. and "Oftener" in the UK, but both are accepted as correct by many educated native speakers and language experts, according to some forums I referred to.