21242491 has 2 divisors, whose sum is σ = 21242492. Its totient is φ = 21242490.

The previous prime is 21242479. The next prime is 21242509. The reversal of 21242491 is 19424212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21242491 - 2¹³ = 21234299 is a prime.

It is not a weakly prime, because it can be changed into another prime (21242461) 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, 10621245 + 10621246.

It is an arithmetic number, because the mean of its divisors is an integer number (10621246).

Almost surely, 2^21242491 is an apocalyptic number.

21242491 is a deficient number, since it is larger than the sum of its proper divisors (1).

21242491 is an equidigital number, since it uses as much as digits as its factorization.

21242491 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1152, while the sum is 25.

The square root of 21242491 is about 4608.9576912790. The cubic root of 21242491 is about 276.9502836656.

The spelling of 21242491 in words is "twenty-one million, two hundred forty-two thousand, four hundred ninety-one".