21745991 has 2 divisors, whose sum is σ = 21745992. Its totient is φ = 21745990.

The previous prime is 21745987. The next prime is 21746029. The reversal of 21745991 is 19954712.

It is an a-pointer prime, because the next prime (21746029) can be obtained adding 21745991 to its sum of digits (38).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21745991 - 2² = 21745987 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21745901) 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, 10872995 + 10872996.

It is an arithmetic number, because the mean of its divisors is an integer number (10872996).

Almost surely, 2^21745991 is an apocalyptic number.

21745991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21745991 is an equidigital number, since it uses as much as digits as its factorization.

21745991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 22680, while the sum is 38.

The square root of 21745991 is about 4663.2596968215. The cubic root of 21745991 is about 279.1213570880.

The spelling of 21745991 in words is "twenty-one million, seven hundred forty-five thousand, nine hundred ninety-one".