21955531 has 4 divisors (see below), whose sum is σ = 23644432. Its totient is φ = 20266632.

The previous prime is 21955463. The next prime is 21955559. The reversal of 21955531 is 13555912.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21955531 - 2¹³ = 21947339 is a prime.

It is a super-2 number, since 2×21955531² = 964090682983922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21955493 and 21955502.

It is not an unprimeable number, because it can be changed into a prime (21955231) 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 3 ways as a sum of consecutive naturals, for example, 844431 + ... + 844456.

It is an arithmetic number, because the mean of its divisors is an integer number (5911108).

Almost surely, 2^21955531 is an apocalyptic number.

21955531 is a deficient number, since it is larger than the sum of its proper divisors (1688901).

21955531 is a wasteful number, since it uses less digits than its factorization.

21955531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1688900.

The product of its digits is 6750, while the sum is 31.

The square root of 21955531 is about 4685.6729506017. The cubic root of 21955531 is about 280.0150119502.

It can be divided in two parts, 219555 and 31, that multiplied together give a triangular number (6806205 = T₃₆₈₉).

The spelling of 21955531 in words is "twenty-one million, nine hundred fifty-five thousand, five hundred thirty-one".