20987321 has 2 divisors, whose sum is σ = 20987322. Its totient is φ = 20987320.

The previous prime is 20987287. The next prime is 20987353. The reversal of 20987321 is 12378902.

It is an a-pointer prime, because the next prime (20987353) can be obtained adding 20987321 to its sum of digits (32).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18181696 + 2805625 = 4264^2 + 1675^2 .

It is a cyclic number.

It is not a de Polignac number, because 20987321 - 2⁶ = 20987257 is a prime.

It is not a weakly prime, because it can be changed into another prime (20987821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10493660 + 10493661.

It is an arithmetic number, because the mean of its divisors is an integer number (10493661).

Almost surely, 2^20987321 is an apocalyptic number.

It is an amenable number.

20987321 is a deficient number, since it is larger than the sum of its proper divisors (1).

20987321 is an equidigital number, since it uses as much as digits as its factorization.

20987321 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6048, while the sum is 32.

The square root of 20987321 is about 4581.1920937677. The cubic root of 20987321 is about 275.8368820160.

The spelling of 20987321 in words is "twenty million, nine hundred eighty-seven thousand, three hundred twenty-one".