21553247 has 2 divisors, whose sum is σ = 21553248. Its totient is φ = 21553246.

The previous prime is 21553243. The next prime is 21553261. The reversal of 21553247 is 74235512.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21553247 - 2² = 21553243 is a prime.

It is equal to p_1362728 and since 21553247 and 1362728 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21553243) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10776623 + 10776624.

It is an arithmetic number, because the mean of its divisors is an integer number (10776624).

Almost surely, 2^21553247 is an apocalyptic number.

21553247 is a deficient number, since it is larger than the sum of its proper divisors (1).

21553247 is an equidigital number, since it uses as much as digits as its factorization.

21553247 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8400, while the sum is 29.

The square root of 21553247 is about 4642.5474687934. The cubic root of 21553247 is about 278.2942513482.

Adding to 21553247 its reverse (74235512), we get a palindrome (95788759).

The spelling of 21553247 in words is "twenty-one million, five hundred fifty-three thousand, two hundred forty-seven".