20681021 has 2 divisors, whose sum is σ = 20681022. Its totient is φ = 20681020.

The previous prime is 20681009. The next prime is 20681029. The reversal of 20681021 is 12018602.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11978521 + 8702500 = 3461^2 + 2950^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20681021 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 20680984 and 20681002.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20681029) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10340510 + 10340511.

It is an arithmetic number, because the mean of its divisors is an integer number (10340511).

Almost surely, 2^20681021 is an apocalyptic number.

It is an amenable number.

20681021 is a deficient number, since it is larger than the sum of its proper divisors (1).

20681021 is an equidigital number, since it uses as much as digits as its factorization.

20681021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 192, while the sum is 20.

The square root of 20681021 is about 4547.6390577969. The cubic root of 20681021 is about 274.4883975795.

Adding to 20681021 its reverse (12018602), we get a palindrome (32699623).

The spelling of 20681021 in words is "twenty million, six hundred eighty-one thousand, twenty-one".