21640427 has 2 divisors, whose sum is σ = 21640428. Its totient is φ = 21640426.

The previous prime is 21640379. The next prime is 21640441. The reversal of 21640427 is 72404612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21640427 - 2⁶ = 21640363 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21640396 and 21640405.

It is not a weakly prime, because it can be changed into another prime (21640457) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10820213 + 10820214.

It is an arithmetic number, because the mean of its divisors is an integer number (10820214).

Almost surely, 2^21640427 is an apocalyptic number.

21640427 is a deficient number, since it is larger than the sum of its proper divisors (1).

21640427 is an equidigital number, since it uses as much as digits as its factorization.

21640427 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2688, while the sum is 26.

The square root of 21640427 is about 4651.9272350285. The cubic root of 21640427 is about 278.6689675782.

The spelling of 21640427 in words is "twenty-one million, six hundred forty thousand, four hundred twenty-seven".