21681531 has 12 divisors (see below), whose sum is σ = 32398080. Its totient is φ = 13955760.

The previous prime is 21681529. The next prime is 21681533. The reversal of 21681531 is 13518612.

It is an interprime number because it is at equal distance from previous prime (21681529) and next prime (21681533).

It is not a de Polignac number, because 21681531 - 2¹ = 21681529 is a prime.

It is a super-2 number, since 2×21681531² = 940177573007922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21681495 and 21681504.

It is not an unprimeable number, because it can be changed into a prime (21681533) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 41275 + ... + 41796.

It is an arithmetic number, because the mean of its divisors is an integer number (2699840).

Almost surely, 2^21681531 is an apocalyptic number.

21681531 is a deficient number, since it is larger than the sum of its proper divisors (10716549).

21681531 is a wasteful number, since it uses less digits than its factorization.

21681531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 83106 (or 83103 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 21681531 is about 4656.3430930291. The cubic root of 21681531 is about 278.8452913430.

The spelling of 21681531 in words is "twenty-one million, six hundred eighty-one thousand, five hundred thirty-one".