21537541 has 2 divisors, whose sum is σ = 21537542. Its totient is φ = 21537540.

The previous prime is 21537497. The next prime is 21537547. The reversal of 21537541 is 14573512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18096516 + 3441025 = 4254^2 + 1855^2 .

It is a cyclic number.

It is not a de Polignac number, because 21537541 - 2⁹ = 21537029 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21537547) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10768770 + 10768771.

It is an arithmetic number, because the mean of its divisors is an integer number (10768771).

Almost surely, 2^21537541 is an apocalyptic number.

It is an amenable number.

21537541 is a deficient number, since it is larger than the sum of its proper divisors (1).

21537541 is an equidigital number, since it uses as much as digits as its factorization.

21537541 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4200, while the sum is 28.

The square root of 21537541 is about 4640.8556323161. The cubic root of 21537541 is about 278.2266366072.

The spelling of 21537541 in words is "twenty-one million, five hundred thirty-seven thousand, five hundred forty-one".