16420721 has 2 divisors, whose sum is σ = 16420722. Its totient is φ = 16420720.

The previous prime is 16420709. The next prime is 16420739. The reversal of 16420721 is 12702461.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14137600 + 2283121 = 3760^2 + 1511^2 .

It is a cyclic number.

It is not a de Polignac number, because 16420721 - 2¹⁸ = 16158577 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (16420751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8210360 + 8210361.

It is an arithmetic number, because the mean of its divisors is an integer number (8210361).

Almost surely, 2^16420721 is an apocalyptic number.

It is an amenable number.

16420721 is a deficient number, since it is larger than the sum of its proper divisors (1).

16420721 is an equidigital number, since it uses as much as digits as its factorization.

16420721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 672, while the sum is 23.

The square root of 16420721 is about 4052.2488817939. The cubic root of 16420721 is about 254.1737759306.

The spelling of 16420721 in words is "sixteen million, four hundred twenty thousand, seven hundred twenty-one".