21801531 has 32 divisors (see below), whose sum is σ = 32832000. Its totient is φ = 12787200.

The previous prime is 21801517. The next prime is 21801553. The reversal of 21801531 is 13510812.

It is not a de Polignac number, because 21801531 - 2⁵ = 21801499 is a prime.

It is a super-2 number, since 2×21801531² = 950613507887922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21801498 and 21801507.

It is not an unprimeable number, because it can be changed into a prime (21801511) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 144306 + ... + 144456.

It is an arithmetic number, because the mean of its divisors is an integer number (1026000).

Almost surely, 2^21801531 is an apocalyptic number.

21801531 is a deficient number, since it is larger than the sum of its proper divisors (11030469).

21801531 is a wasteful number, since it uses less digits than its factorization.

21801531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 339.

The product of its (nonzero) digits is 240, while the sum is 21.

The square root of 21801531 is about 4669.2109611796. The cubic root of 21801531 is about 279.3587835479.

The spelling of 21801531 in words is "twenty-one million, eight hundred one thousand, five hundred thirty-one".