21273991 has 2 divisors, whose sum is σ = 21273992. Its totient is φ = 21273990.

The previous prime is 21273961. The next prime is 21273997. The reversal of 21273991 is 19937212.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21273991 - 2⁹ = 21273479 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21273997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10636995 + 10636996.

It is an arithmetic number, because the mean of its divisors is an integer number (10636996).

Almost surely, 2^21273991 is an apocalyptic number.

21273991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21273991 is an equidigital number, since it uses as much as digits as its factorization.

21273991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6804, while the sum is 34.

The square root of 21273991 is about 4612.3736839072. The cubic root of 21273991 is about 277.0871104516.

The spelling of 21273991 in words is "twenty-one million, two hundred seventy-three thousand, nine hundred ninety-one".