Consider the image attached, showing a part of the options chain for the NDX expiring July 20. What can possible explain such large differences in Open Interest across similar strikes, e.g. 818 at 7,400 and 61 for 7,410? 
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$\begingroup$ Have you looked which ones have the biggest volume? Usually OI is linked to Vol. And the ones you highlight have rounded strikes so likely the market has an affinity to these instruments $\endgroup$ – Attack68♦ Jul 19 '18 at 21:08
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There's not anything to explain once you realise that people like round numbers.
