21039971 has 2 divisors, whose sum is σ = 21039972. Its totient is φ = 21039970.

The previous prime is 21039961. The next prime is 21039989. The reversal of 21039971 is 17993012.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21039971 is a prime.

It is not a weakly prime, because it can be changed into another prime (21039901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10519985 + 10519986.

It is an arithmetic number, because the mean of its divisors is an integer number (10519986).

Almost surely, 2^21039971 is an apocalyptic number.

21039971 is a deficient number, since it is larger than the sum of its proper divisors (1).

21039971 is an equidigital number, since it uses as much as digits as its factorization.

21039971 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3402, while the sum is 32.

The square root of 21039971 is about 4586.9348153206. The cubic root of 21039971 is about 276.0673494886.

The spelling of 21039971 in words is "twenty-one million, thirty-nine thousand, nine hundred seventy-one".