21505451 has 12 divisors (see below), whose sum is σ = 23774016. Its totient is φ = 19438320.

The previous prime is 21505447. The next prime is 21505469. The reversal of 21505451 is 15450512.

It is a happy number.

It is not a de Polignac number, because 21505451 - 2² = 21505447 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21505481) 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 in 11 ways as a sum of consecutive naturals, for example, 26585 + ... + 27381.

It is an arithmetic number, because the mean of its divisors is an integer number (1981168).

Almost surely, 2^21505451 is an apocalyptic number.

21505451 is a deficient number, since it is larger than the sum of its proper divisors (2268565).

21505451 is a wasteful number, since it uses less digits than its factorization.

21505451 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1042 (or 1031 counting only the distinct ones).

The product of its (nonzero) digits is 1000, while the sum is 23.

The square root of 21505451 is about 4637.3970069426. The cubic root of 21505451 is about 278.0883860567.

Adding to 21505451 its reverse (15450512), we get a palindrome (36955963).

The spelling of 21505451 in words is "twenty-one million, five hundred five thousand, four hundred fifty-one".