21001251 has 8 divisors (see below), whose sum is σ = 29475520. Its totient is φ = 13263912.

The previous prime is 21001247. The next prime is 21001319. The reversal of 21001251 is 15210012.

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

It is not a de Polignac number, because 21001251 - 2² = 21001247 is a prime.

It is a Duffinian 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 7 ways as a sum of consecutive naturals, for example, 184165 + ... + 184278.

It is an arithmetic number, because the mean of its divisors is an integer number (3684440).

Almost surely, 2^21001251 is an apocalyptic number.

21001251 is a deficient number, since it is larger than the sum of its proper divisors (8474269).

21001251 is a wasteful number, since it uses less digits than its factorization.

21001251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 368465.

The product of its (nonzero) digits is 20, while the sum is 12.

The square root of 21001251 is about 4582.7121882134. The cubic root of 21001251 is about 275.8978959645.

Adding to 21001251 its reverse (15210012), we get a palindrome (36211263).

The spelling of 21001251 in words is "twenty-one million, one thousand, two hundred fifty-one".