21021953 has 2 divisors, whose sum is σ = 21021954. Its totient is φ = 21021952.

The previous prime is 21021899. The next prime is 21021989. The reversal of 21021953 is 35912012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14010049 + 7011904 = 3743^2 + 2648^2 .

It is a cyclic number.

It is not a de Polignac number, because 21021953 - 2⁸ = 21021697 is a prime.

It is equal to p_1331285 and since 21021953 and 1331285 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21021053) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510976 + 10510977.

It is an arithmetic number, because the mean of its divisors is an integer number (10510977).

Almost surely, 2^21021953 is an apocalyptic number.

It is an amenable number.

21021953 is a deficient number, since it is larger than the sum of its proper divisors (1).

21021953 is an equidigital number, since it uses as much as digits as its factorization.

21021953 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21021953 is about 4584.9703379629. The cubic root of 21021953 is about 275.9885217169.

Adding to 21021953 its reverse (35912012), we get a palindrome (56933965).

The spelling of 21021953 in words is "twenty-one million, twenty-one thousand, nine hundred fifty-three".