21538061 has 2 divisors, whose sum is σ = 21538062. Its totient is φ = 21538060.

The previous prime is 21538043. The next prime is 21538067. The reversal of 21538061 is 16083512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15132100 + 6405961 = 3890^2 + 2531^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21538061 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21538061.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21538067) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10769030 + 10769031.

It is an arithmetic number, because the mean of its divisors is an integer number (10769031).

Almost surely, 2^21538061 is an apocalyptic number.

It is an amenable number.

21538061 is a deficient number, since it is larger than the sum of its proper divisors (1).

21538061 is an equidigital number, since it uses as much as digits as its factorization.

21538061 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1440, while the sum is 26.

The square root of 21538061 is about 4640.9116561296. The cubic root of 21538061 is about 278.2288757469.

The spelling of 21538061 in words is "twenty-one million, five hundred thirty-eight thousand, sixty-one".