21687373 has 2 divisors, whose sum is σ = 21687374. Its totient is φ = 21687372.

The previous prime is 21687361. The next prime is 21687473. The reversal of 21687373 is 37378612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13410244 + 8277129 = 3662^2 + 2877^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21687373 is a prime.

It is a super-2 number, since 2×21687373² = 940684295282258, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21687343) 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, 10843686 + 10843687.

It is an arithmetic number, because the mean of its divisors is an integer number (10843687).

Almost surely, 2^21687373 is an apocalyptic number.

It is an amenable number.

21687373 is a deficient number, since it is larger than the sum of its proper divisors (1).

21687373 is an equidigital number, since it uses as much as digits as its factorization.

21687373 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 42336, while the sum is 37.

The square root of 21687373 is about 4656.9703670949. The cubic root of 21687373 is about 278.8703336691.

The spelling of 21687373 in words is "twenty-one million, six hundred eighty-seven thousand, three hundred seventy-three".