21145991 has 2 divisors, whose sum is σ = 21145992. Its totient is φ = 21145990.

The previous prime is 21145987. The next prime is 21146023. The reversal of 21145991 is 19954112.

It is an a-pointer prime, because the next prime (21146023) can be obtained adding 21145991 to its sum of digits (32).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21145991 - 2² = 21145987 is a prime.

It is a Sophie Germain prime.

It is equal to p_1338629 and since 21145991 and 1338629 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21145921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10572995 + 10572996.

It is an arithmetic number, because the mean of its divisors is an integer number (10572996).

Almost surely, 2^21145991 is an apocalyptic number.

21145991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21145991 is an equidigital number, since it uses as much as digits as its factorization.

21145991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3240, while the sum is 32.

The square root of 21145991 is about 4598.4770304961. The cubic root of 21145991 is about 276.5302721189.

The spelling of 21145991 in words is "twenty-one million, one hundred forty-five thousand, nine hundred ninety-one".