21615287 has 2 divisors, whose sum is σ = 21615288. Its totient is φ = 21615286.

The previous prime is 21615247. The next prime is 21615301. The reversal of 21615287 is 78251612.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21615287 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21615247) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10807643 + 10807644.

It is an arithmetic number, because the mean of its divisors is an integer number (10807644).

Almost surely, 2^21615287 is an apocalyptic number.

21615287 is a deficient number, since it is larger than the sum of its proper divisors (1).

21615287 is an equidigital number, since it uses as much as digits as its factorization.

21615287 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6720, while the sum is 32.

The square root of 21615287 is about 4649.2243439094. The cubic root of 21615287 is about 278.5610144944.

Adding to 21615287 its reverse (78251612), we get a palindrome (99866899).

The spelling of 21615287 in words is "twenty-one million, six hundred fifteen thousand, two hundred eighty-seven".