21250081 has 8 divisors (see below), whose sum is σ = 21770504. Its totient is φ = 20736000.

The previous prime is 21250067. The next prime is 21250111. The reversal of 21250081 is 18005212.

It can be written as a sum of positive squares in 4 ways, for example, as 3534400 + 17715681 = 1880^2 + 4209^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a 3-Lehmer number, since φ(21250081) divides (21250081-1)³.

It is a cyclic number.

It is not a de Polignac number, because 21250081 - 2¹³ = 21241889 is a prime.

It is a super-2 number, since 2×21250081² = 903131885013122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21250001) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5581 + ... + 8581.

It is an arithmetic number, because the mean of its divisors is an integer number (2721313).

Almost surely, 2^21250081 is an apocalyptic number.

It is an amenable number.

21250081 is a deficient number, since it is larger than the sum of its proper divisors (520423).

21250081 is an equidigital number, since it uses as much as digits as its factorization.

21250081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3171.

The product of its (nonzero) digits is 160, while the sum is 19.

The square root of 21250081 is about 4609.7810143216. The cubic root of 21250081 is about 276.9832647685.

Adding to 21250081 its reverse (18005212), we get a palindrome (39255293).

The spelling of 21250081 in words is "twenty-one million, two hundred fifty thousand, eighty-one".