21420556 has 6 divisors (see below), whose sum is σ = 37485980. Its totient is φ = 10710276.

The previous prime is 21420551. The next prime is 21420563. The reversal of 21420556 is 65502412.

It is a self number, because there is not a number n which added to its sum of digits gives 21420556.

It is not an unprimeable number, because it can be changed into a prime (21420551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2677566 + ... + 2677573.

Almost surely, 2^21420556 is an apocalyptic number.

It is an amenable number.

21420556 is a deficient number, since it is larger than the sum of its proper divisors (16065424).

21420556 is a wasteful number, since it uses less digits than its factorization.

21420556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5355143 (or 5355141 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 25.

The square root of 21420556 is about 4628.2346526511. The cubic root of 21420556 is about 277.7219758961.

Adding to 21420556 its reverse (65502412), we get a palindrome (86922968).

The spelling of 21420556 in words is "twenty-one million, four hundred twenty thousand, five hundred fifty-six".