21563137 has 2 divisors, whose sum is σ = 21563138. Its totient is φ = 21563136.

The previous prime is 21563117. The next prime is 21563147. The reversal of 21563137 is 73136512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19927296 + 1635841 = 4464^2 + 1279^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21563137 is a prime.

It is not a weakly prime, because it can be changed into another prime (21563117) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10781568 + 10781569.

It is an arithmetic number, because the mean of its divisors is an integer number (10781569).

Almost surely, 2^21563137 is an apocalyptic number.

It is an amenable number.

21563137 is a deficient number, since it is larger than the sum of its proper divisors (1).

21563137 is an equidigital number, since it uses as much as digits as its factorization.

21563137 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3780, while the sum is 28.

The square root of 21563137 is about 4643.6124945994. The cubic root of 21563137 is about 278.3368112043.

Adding to 21563137 its reverse (73136512), we get a palindrome (94699649).

The spelling of 21563137 in words is "twenty-one million, five hundred sixty-three thousand, one hundred thirty-seven".