20978021 has 2 divisors, whose sum is σ = 20978022. Its totient is φ = 20978020.

The previous prime is 20978011. The next prime is 20978077. The reversal of 20978021 is 12087902.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18369796 + 2608225 = 4286^2 + 1615^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20978021 is a prime.

It is equal to p_1328627 and since 20978021 and 1328627 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20978011) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10489010 + 10489011.

It is an arithmetic number, because the mean of its divisors is an integer number (10489011).

Almost surely, 2^20978021 is an apocalyptic number.

It is an amenable number.

20978021 is a deficient number, since it is larger than the sum of its proper divisors (1).

20978021 is an equidigital number, since it uses as much as digits as its factorization.

20978021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2016, while the sum is 29.

The square root of 20978021 is about 4580.1769616468. The cubic root of 20978021 is about 275.7961326193.

The spelling of 20978021 in words is "twenty million, nine hundred seventy-eight thousand, twenty-one".