21720481 has 2 divisors, whose sum is σ = 21720482. Its totient is φ = 21720480.

The previous prime is 21720473. The next prime is 21720499. The reversal of 21720481 is 18402712.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14745600 + 6974881 = 3840^2 + 2641^2 .

It is a cyclic number.

It is not a de Polignac number, because 21720481 - 2³ = 21720473 is a prime.

It is a super-2 number, since 2×21720481² = 943558589742722, which contains 22 as substring.

It is equal to p_1372651 and since 21720481 and 1372651 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21720431) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10860240 + 10860241.

It is an arithmetic number, because the mean of its divisors is an integer number (10860241).

Almost surely, 2^21720481 is an apocalyptic number.

It is an amenable number.

21720481 is a deficient number, since it is larger than the sum of its proper divisors (1).

21720481 is an equidigital number, since it uses as much as digits as its factorization.

21720481 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 21720481 is about 4660.5236830210. The cubic root of 21720481 is about 279.0121695766.

It can be divided in two parts, 21720 and 481, that added together give a square (22201 = 149²).

The spelling of 21720481 in words is "twenty-one million, seven hundred twenty thousand, four hundred eighty-one".