21500251 has 2 divisors, whose sum is σ = 21500252. Its totient is φ = 21500250.

The previous prime is 21500231. The next prime is 21500261. The reversal of 21500251 is 15200512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21500251 - 2¹¹ = 21498203 is a prime.

It is not a weakly prime, because it can be changed into another prime (21500231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10750125 + 10750126.

It is an arithmetic number, because the mean of its divisors is an integer number (10750126).

Almost surely, 2^21500251 is an apocalyptic number.

21500251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21500251 is an equidigital number, since it uses as much as digits as its factorization.

21500251 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 100, while the sum is 16.

The square root of 21500251 is about 4636.8363136949. The cubic root of 21500251 is about 278.0659704038.

Adding to 21500251 its reverse (15200512), we get a palindrome (36700763).

The spelling of 21500251 in words is "twenty-one million, five hundred thousand, two hundred fifty-one".