21209178251 has 2 divisors, whose sum is σ = 21209178252. Its totient is φ = 21209178250.

The previous prime is 21209178187. The next prime is 21209178293. The reversal of 21209178251 is 15287190212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21209178251 - 2⁶ = 21209178187 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21209118251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10604589125 + 10604589126.

It is an arithmetic number, because the mean of its divisors is an integer number (10604589126).

Almost surely, 2^21209178251 is an apocalyptic number.

21209178251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21209178251 is an equidigital number, since it uses as much as digits as its factorization.

21209178251 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 20160, while the sum is 38.

The spelling of 21209178251 in words is "twenty-one billion, two hundred nine million, one hundred seventy-eight thousand, two hundred fifty-one".