21000253 has 4 divisors (see below), whose sum is σ = 22235580. Its totient is φ = 19764928.

The previous prime is 21000251. The next prime is 21000269. The reversal of 21000253 is 35200012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7064964 + 13935289 = 2658^2 + 3733^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000253 - 2¹ = 21000251 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000251) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 617638 + ... + 617671.

It is an arithmetic number, because the mean of its divisors is an integer number (5558895).

Almost surely, 2^21000253 is an apocalyptic number.

It is an amenable number.

21000253 is a deficient number, since it is larger than the sum of its proper divisors (1235327).

21000253 is a wasteful number, since it uses less digits than its factorization.

21000253 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1235326.

The product of its (nonzero) digits is 60, while the sum is 13.

The square root of 21000253 is about 4582.6032994358. The cubic root of 21000253 is about 275.8935255826.

Adding to 21000253 its reverse (35200012), we get a palindrome (56200265).

The spelling of 21000253 in words is "twenty-one million, two hundred fifty-three", and thus it is an aban number.