21681533 has 2 divisors, whose sum is σ = 21681534. Its totient is φ = 21681532.

The previous prime is 21681529. The next prime is 21681547. The reversal of 21681533 is 33518612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10936249 + 10745284 = 3307^2 + 3278^2 .

It is a cyclic number.

It is not a de Polignac number, because 21681533 - 2² = 21681529 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21681496 and 21681505.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21681553) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10840766 + 10840767.

It is an arithmetic number, because the mean of its divisors is an integer number (10840767).

Almost surely, 2^21681533 is an apocalyptic number.

It is an amenable number.

21681533 is a deficient number, since it is larger than the sum of its proper divisors (1).

21681533 is an equidigital number, since it uses as much as digits as its factorization.

21681533 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4320, while the sum is 29.

The square root of 21681533 is about 4656.3433077899. The cubic root of 21681533 is about 278.8452999170.

The spelling of 21681533 in words is "twenty-one million, six hundred eighty-one thousand, five hundred thirty-three".