56

This number is a composite.

Just showing those entries submitted by 'Firoozbakht': (Click here to show all)

56 = sigma(sigma(sigma(5+6))). 56 is the smallest multidigit number with this property and there is only one other. [Firoozbakht]

prime(56) = prime(5)*prime(6)+sigma(56). 56 is the only known number (up to 3*10^8) with this property. [Firoozbakht]