21700251 has 16 divisors (see below), whose sum is σ = 32897920. Its totient is φ = 14129640.

The previous prime is 21700243. The next prime is 21700253. The reversal of 21700251 is 15200712.

It is not a de Polignac number, because 21700251 - 2³ = 21700243 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21700253) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8185 + ... + 10506.

It is an arithmetic number, because the mean of its divisors is an integer number (2056120).

Almost surely, 2^21700251 is an apocalyptic number.

21700251 is a deficient number, since it is larger than the sum of its proper divisors (11197669).

21700251 is a wasteful number, since it uses less digits than its factorization.

21700251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18743 (or 18737 counting only the distinct ones).

The product of its (nonzero) digits is 140, while the sum is 18.

The square root of 21700251 is about 4658.3528204721. The cubic root of 21700251 is about 278.9255206443.

Adding to 21700251 its reverse (15200712), we get a palindrome (36900963).

The spelling of 21700251 in words is "twenty-one million, seven hundred thousand, two hundred fifty-one".