21553531 has 2 divisors, whose sum is σ = 21553532. Its totient is φ = 21553530.

The previous prime is 21553529. The next prime is 21553613. The reversal of 21553531 is 13535512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21553531 - 2¹ = 21553529 is a prime.

It is a super-2 number, since 2×21553531² = 929109397135922, which contains 22 as substring.

Together with 21553529, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 21553496 and 21553505.

It is not a weakly prime, because it can be changed into another prime (21557531) 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 as a sum of consecutive naturals, namely, 10776765 + 10776766.

It is an arithmetic number, because the mean of its divisors is an integer number (10776766).

Almost surely, 2^21553531 is an apocalyptic number.

21553531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21553531 is an equidigital number, since it uses as much as digits as its factorization.

21553531 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2250, while the sum is 25.

The square root of 21553531 is about 4642.5780553481. The cubic root of 21553531 is about 278.2954736733.

The spelling of 21553531 in words is "twenty-one million, five hundred fifty-three thousand, five hundred thirty-one".