21247861 has 2 divisors, whose sum is σ = 21247862. Its totient is φ = 21247860.

The previous prime is 21247843. The next prime is 21247867. The reversal of 21247861 is 16874212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20875761 + 372100 = 4569^2 + 610^2 .

It is a cyclic number.

It is not a de Polignac number, because 21247861 - 2²¹ = 19150709 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21247867) 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, 10623930 + 10623931.

It is an arithmetic number, because the mean of its divisors is an integer number (10623931).

Almost surely, 2^21247861 is an apocalyptic number.

It is an amenable number.

21247861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21247861 is an equidigital number, since it uses as much as digits as its factorization.

21247861 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5376, while the sum is 31.

The square root of 21247861 is about 4609.5402156831. The cubic root of 21247861 is about 276.9736189345.

The spelling of 21247861 in words is "twenty-one million, two hundred forty-seven thousand, eight hundred sixty-one".