21523531 has 2 divisors, whose sum is σ = 21523532. Its totient is φ = 21523530.

The previous prime is 21523519. The next prime is 21523543. The reversal of 21523531 is 13532512.

It is a balanced prime because it is at equal distance from previous prime (21523519) and next prime (21523543).

It is a cyclic number.

It is not a de Polignac number, because 21523531 - 2⁵ = 21523499 is a prime.

It is a super-4 number, since 4×21523531⁴ (a number of 30 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is not a weakly prime, because it can be changed into another prime (21523511) 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 as a sum of consecutive naturals, namely, 10761765 + 10761766.

It is an arithmetic number, because the mean of its divisors is an integer number (10761766).

Almost surely, 2^21523531 is an apocalyptic number.

21523531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21523531 is an equidigital number, since it uses as much as digits as its factorization.

21523531 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 900, while the sum is 22.

The square root of 21523531 is about 4639.3459668363. The cubic root of 21523531 is about 278.1662954463.

The spelling of 21523531 in words is "twenty-one million, five hundred twenty-three thousand, five hundred thirty-one".