21720047 has 2 divisors, whose sum is σ = 21720048. Its totient is φ = 21720046.

The previous prime is 21720007. The next prime is 21720053. The reversal of 21720047 is 74002712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21720047 - 2¹⁰ = 21719023 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21720007) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10860023 + 10860024.

It is an arithmetic number, because the mean of its divisors is an integer number (10860024).

Almost surely, 2^21720047 is an apocalyptic number.

21720047 is a deficient number, since it is larger than the sum of its proper divisors (1).

21720047 is an equidigital number, since it uses as much as digits as its factorization.

21720047 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 784, while the sum is 23.

The square root of 21720047 is about 4660.4771214973. The cubic root of 21720047 is about 279.0103112370.

Adding to 21720047 its reverse (74002712), we get a palindrome (95722759).

The spelling of 21720047 in words is "twenty-one million, seven hundred twenty thousand, forty-seven".