21231971 has 2 divisors, whose sum is σ = 21231972. Its totient is φ = 21231970.

The previous prime is 21231941. The next prime is 21231979. The reversal of 21231971 is 17913212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21231971 - 2¹⁰ = 21230947 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21231971.

It is not a weakly prime, because it can be changed into another prime (21231979) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10615985 + 10615986.

It is an arithmetic number, because the mean of its divisors is an integer number (10615986).

Almost surely, 2^21231971 is an apocalyptic number.

21231971 is a deficient number, since it is larger than the sum of its proper divisors (1).

21231971 is an equidigital number, since it uses as much as digits as its factorization.

21231971 is an evil number, because the sum of its binary digits is even.

The product of its digits is 756, while the sum is 26.

The square root of 21231971 is about 4607.8162940812. The cubic root of 21231971 is about 276.9045577339.

The spelling of 21231971 in words is "twenty-one million, two hundred thirty-one thousand, nine hundred seventy-one".