21261251 has 4 divisors (see below), whose sum is σ = 23194104. Its totient is φ = 19328400.

The previous prime is 21261241. The next prime is 21261259. The reversal of 21261251 is 15216212.

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

It is a cyclic number.

It is not a de Polignac number, because 21261251 - 2⁶ = 21261187 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21261259) 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, 966410 + ... + 966431.

It is an arithmetic number, because the mean of its divisors is an integer number (5798526).

Almost surely, 2^21261251 is an apocalyptic number.

21261251 is a deficient number, since it is larger than the sum of its proper divisors (1932853).

21261251 is a wasteful number, since it uses less digits than its factorization.

21261251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1932852.

The product of its digits is 240, while the sum is 20.

The square root of 21261251 is about 4610.9924094494. The cubic root of 21261251 is about 277.0317878954.

Adding to 21261251 its reverse (15216212), we get a palindrome (36477463).

It can be divided in two parts, 21261 and 251, that added together give a palindrome (21512).

The spelling of 21261251 in words is "twenty-one million, two hundred sixty-one thousand, two hundred fifty-one".