21523387 has 2 divisors, whose sum is σ = 21523388. Its totient is φ = 21523386.

The previous prime is 21523361. The next prime is 21523391. The reversal of 21523387 is 78332512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21523387 is a prime.

It is not a weakly prime, because it can be changed into another prime (21521387) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10761693 + 10761694.

It is an arithmetic number, because the mean of its divisors is an integer number (10761694).

Almost surely, 2^21523387 is an apocalyptic number.

21523387 is a deficient number, since it is larger than the sum of its proper divisors (1).

21523387 is an equidigital number, since it uses as much as digits as its factorization.

21523387 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10080, while the sum is 31.

The square root of 21523387 is about 4639.3304473814. The cubic root of 21523387 is about 278.1656751014.

Adding to 21523387 its reverse (78332512), we get a palindrome (99855899).

It can be divided in two parts, 215 and 23387, that multiplied together give a palindrome (5028205).

The spelling of 21523387 in words is "twenty-one million, five hundred twenty-three thousand, three hundred eighty-seven".