21531989 has 2 divisors, whose sum is σ = 21531990. Its totient is φ = 21531988.

The previous prime is 21531977. The next prime is 21532019. The reversal of 21531989 is 98913512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13380964 + 8151025 = 3658^2 + 2855^2 .

It is a cyclic number.

It is not a de Polignac number, because 21531989 - 2⁴ = 21531973 is a prime.

It is a super-2 number, since 2×21531989² = 927253100592242, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21531689) 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, 10765994 + 10765995.

It is an arithmetic number, because the mean of its divisors is an integer number (10765995).

Almost surely, 2^21531989 is an apocalyptic number.

It is an amenable number.

21531989 is a deficient number, since it is larger than the sum of its proper divisors (1).

21531989 is an equidigital number, since it uses as much as digits as its factorization.

21531989 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 19440, while the sum is 38.

The square root of 21531989 is about 4640.2574282037. The cubic root of 21531989 is about 278.2027272383.

The spelling of 21531989 in words is "twenty-one million, five hundred thirty-one thousand, nine hundred eighty-nine".