21556481 has 2 divisors, whose sum is σ = 21556482. Its totient is φ = 21556480.

The previous prime is 21556477. The next prime is 21556489. The reversal of 21556481 is 18465512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21242881 + 313600 = 4609^2 + 560^2 .

It is a cyclic number.

It is not a de Polignac number, because 21556481 - 2² = 21556477 is a prime.

It is a super-2 number, since 2×21556481² = 929363746206722, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21556489) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778240 + 10778241.

It is an arithmetic number, because the mean of its divisors is an integer number (10778241).

Almost surely, 2^21556481 is an apocalyptic number.

It is an amenable number.

21556481 is a deficient number, since it is larger than the sum of its proper divisors (1).

21556481 is an equidigital number, since it uses as much as digits as its factorization.

21556481 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9600, while the sum is 32.

The square root of 21556481 is about 4642.8957558834. The cubic root of 21556481 is about 278.3081697244.

The spelling of 21556481 in words is "twenty-one million, five hundred fifty-six thousand, four hundred eighty-one".