21640547 has 2 divisors, whose sum is σ = 21640548. Its totient is φ = 21640546.

The previous prime is 21640537. The next prime is 21640559. The reversal of 21640547 is 74504612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21640547 - 2¹⁰ = 21639523 is a prime.

It is not a weakly prime, because it can be changed into another prime (21640537) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10820273 + 10820274.

It is an arithmetic number, because the mean of its divisors is an integer number (10820274).

Almost surely, 2^21640547 is an apocalyptic number.

21640547 is a deficient number, since it is larger than the sum of its proper divisors (1).

21640547 is an equidigital number, since it uses as much as digits as its factorization.

21640547 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6720, while the sum is 29.

The square root of 21640547 is about 4651.9401328908. The cubic root of 21640547 is about 278.6694826668.

The spelling of 21640547 in words is "twenty-one million, six hundred forty thousand, five hundred forty-seven".