20510821 has 2 divisors, whose sum is σ = 20510822. Its totient is φ = 20510820.

The previous prime is 20510797. The next prime is 20510827. The reversal of 20510821 is 12801502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10962721 + 9548100 = 3311^2 + 3090^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20510821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20510827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10255410 + 10255411.

It is an arithmetic number, because the mean of its divisors is an integer number (10255411).

Almost surely, 2^20510821 is an apocalyptic number.

It is an amenable number.

20510821 is a deficient number, since it is larger than the sum of its proper divisors (1).

20510821 is an equidigital number, since it uses as much as digits as its factorization.

20510821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 160, while the sum is 19.

The square root of 20510821 is about 4528.8873909604. The cubic root of 20510821 is about 273.7333305113.

It can be divided in two parts, 205 and 10821, that added together give a triangular number (11026 = T₁₄₈).

The spelling of 20510821 in words is "twenty million, five hundred ten thousand, eight hundred twenty-one".