21687541 has 2 divisors, whose sum is σ = 21687542. Its totient is φ = 21687540.

The previous prime is 21687527. The next prime is 21687553. The reversal of 21687541 is 14578612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18096516 + 3591025 = 4254^2 + 1895^2 .

It is a cyclic number.

It is not a de Polignac number, because 21687541 - 2¹⁹ = 21163253 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21687497 and 21687506.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21687521) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10843770 + 10843771.

It is an arithmetic number, because the mean of its divisors is an integer number (10843771).

Almost surely, 2^21687541 is an apocalyptic number.

It is an amenable number.

21687541 is a deficient number, since it is larger than the sum of its proper divisors (1).

21687541 is an equidigital number, since it uses as much as digits as its factorization.

21687541 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 13440, while the sum is 34.

The square root of 21687541 is about 4656.9884045379. The cubic root of 21687541 is about 278.8710537516.

The spelling of 21687541 in words is "twenty-one million, six hundred eighty-seven thousand, five hundred forty-one".