21284251 has 2 divisors, whose sum is σ = 21284252. Its totient is φ = 21284250.

The previous prime is 21284243. The next prime is 21284273. The reversal of 21284251 is 15248212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21284251 - 2³ = 21284243 is a prime.

It is not a weakly prime, because it can be changed into another prime (21284281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10642125 + 10642126.

It is an arithmetic number, because the mean of its divisors is an integer number (10642126).

Almost surely, 2^21284251 is an apocalyptic number.

21284251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21284251 is an equidigital number, since it uses as much as digits as its factorization.

21284251 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1280, while the sum is 25.

The square root of 21284251 is about 4613.4857754197. The cubic root of 21284251 is about 277.1316477280.

The spelling of 21284251 in words is "twenty-one million, two hundred eighty-four thousand, two hundred fifty-one".