21253957 has 2 divisors, whose sum is σ = 21253958. Its totient is φ = 21253956.

The previous prime is 21253943. The next prime is 21253963. The reversal of 21253957 is 75935212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13586596 + 7667361 = 3686^2 + 2769^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21253957 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21253937) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10626978 + 10626979.

It is an arithmetic number, because the mean of its divisors is an integer number (10626979).

Almost surely, 2^21253957 is an apocalyptic number.

It is an amenable number.

21253957 is a deficient number, since it is larger than the sum of its proper divisors (1).

21253957 is an equidigital number, since it uses as much as digits as its factorization.

21253957 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 18900, while the sum is 34.

The square root of 21253957 is about 4610.2014055787. The cubic root of 21253957 is about 277.0001042630. Note that the first 3 decimals are identical.

The spelling of 21253957 in words is "twenty-one million, two hundred fifty-three thousand, nine hundred fifty-seven".