21256447 has 2 divisors, whose sum is σ = 21256448. Its totient is φ = 21256446.

The previous prime is 21256399. The next prime is 21256457. The reversal of 21256447 is 74465212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21256447 - 2¹¹ = 21254399 is a prime.

It is a plaindrome in base 16.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21256457) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10628223 + 10628224.

It is an arithmetic number, because the mean of its divisors is an integer number (10628224).

Almost surely, 2^21256447 is an apocalyptic number.

21256447 is a deficient number, since it is larger than the sum of its proper divisors (1).

21256447 is an equidigital number, since it uses as much as digits as its factorization.

21256447 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13440, while the sum is 31.

The square root of 21256447 is about 4610.4714509473. The cubic root of 21256447 is about 277.0109211245.

The spelling of 21256447 in words is "twenty-one million, two hundred fifty-six thousand, four hundred forty-seven".