21659251 has 2 divisors, whose sum is σ = 21659252. Its totient is φ = 21659250.

The previous prime is 21659243. The next prime is 21659257. The reversal of 21659251 is 15295612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21659251 - 2³ = 21659243 is a prime.

It is not a weakly prime, because it can be changed into another prime (21659257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10829625 + 10829626.

It is an arithmetic number, because the mean of its divisors is an integer number (10829626).

Almost surely, 2^21659251 is an apocalyptic number.

21659251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21659251 is an equidigital number, since it uses as much as digits as its factorization.

21659251 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5400, while the sum is 31.

The square root of 21659251 is about 4653.9500427057. The cubic root of 21659251 is about 278.7497445486.

The spelling of 21659251 in words is "twenty-one million, six hundred fifty-nine thousand, two hundred fifty-one".