21020971 has 2 divisors, whose sum is σ = 21020972. Its totient is φ = 21020970.

The previous prime is 21020963. The next prime is 21021001. The reversal of 21020971 is 17902012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21020971 - 2³ = 21020963 is a prime.

It is not a weakly prime, because it can be changed into another prime (21020941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510485 + 10510486.

It is an arithmetic number, because the mean of its divisors is an integer number (10510486).

Almost surely, 2^21020971 is an apocalyptic number.

21020971 is a deficient number, since it is larger than the sum of its proper divisors (1).

21020971 is an equidigital number, since it uses as much as digits as its factorization.

21020971 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 252, while the sum is 22.

The square root of 21020971 is about 4584.8632476880. The cubic root of 21020971 is about 275.9842242261.

Adding to 21020971 its reverse (17902012), we get a palindrome (38922983).

The spelling of 21020971 in words is "twenty-one million, twenty thousand, nine hundred seventy-one".