21217747 has 2 divisors, whose sum is σ = 21217748. Its totient is φ = 21217746.

The previous prime is 21217739. The next prime is 21217829. The reversal of 21217747 is 74771212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21217747 - 2³ = 21217739 is a prime.

It is not a weakly prime, because it can be changed into another prime (21277747) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10608873 + 10608874.

It is an arithmetic number, because the mean of its divisors is an integer number (10608874).

Almost surely, 2^21217747 is an apocalyptic number.

21217747 is a deficient number, since it is larger than the sum of its proper divisors (1).

21217747 is an equidigital number, since it uses as much as digits as its factorization.

21217747 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5488, while the sum is 31.

The square root of 21217747 is about 4606.2725711794. The cubic root of 21217747 is about 276.8427080779.

Adding to 21217747 its reverse (74771212), we get a palindrome (95988959).

The spelling of 21217747 in words is "twenty-one million, two hundred seventeen thousand, seven hundred forty-seven".