21440491 has 2 divisors, whose sum is σ = 21440492. Its totient is φ = 21440490.

The previous prime is 21440473. The next prime is 21440527. The reversal of 21440491 is 19404412.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21440491 is a prime.

It is not a weakly prime, because it can be changed into another prime (21440411) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10720245 + 10720246.

It is an arithmetic number, because the mean of its divisors is an integer number (10720246).

Almost surely, 2^21440491 is an apocalyptic number.

21440491 is a deficient number, since it is larger than the sum of its proper divisors (1).

21440491 is an equidigital number, since it uses as much as digits as its factorization.

21440491 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21440491 is about 4630.3877807372. The cubic root of 21440491 is about 277.8081029944.

The spelling of 21440491 in words is "twenty-one million, four hundred forty thousand, four hundred ninety-one".