21404531 has 2 divisors, whose sum is σ = 21404532. Its totient is φ = 21404530.

The previous prime is 21404503. The next prime is 21404543. The reversal of 21404531 is 13540412.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21404531 is a prime.

It is a super-2 number, since 2×21404531² = 916307894659922, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21404561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10702265 + 10702266.

It is an arithmetic number, because the mean of its divisors is an integer number (10702266).

Almost surely, 2^21404531 is an apocalyptic number.

21404531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21404531 is an equidigital number, since it uses as much as digits as its factorization.

21404531 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 480, while the sum is 20.

The square root of 21404531 is about 4626.5031070994. The cubic root of 21404531 is about 277.6527027961.

Adding to 21404531 its reverse (13540412), we get a palindrome (34944943).

The spelling of 21404531 in words is "twenty-one million, four hundred four thousand, five hundred thirty-one".