21121556 has 12 divisors (see below), whose sum is σ = 37344468. Its totient is φ = 10451712.

The previous prime is 21121547. The next prime is 21121603. The reversal of 21121556 is 65512112.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 5597956 + 15523600 = 2366^2 + 3940^2 .

It is a super-2 number, since 2×21121556² = 892240255722272, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26831 + ... + 27606.

It is an arithmetic number, because the mean of its divisors is an integer number (3112039).

Almost surely, 2^21121556 is an apocalyptic number.

It is an amenable number.

21121556 is a deficient number, since it is larger than the sum of its proper divisors (16222912).

21121556 is a wasteful number, since it uses less digits than its factorization.

21121556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 54538 (or 54536 counting only the distinct ones).

The product of its digits is 600, while the sum is 23.

The square root of 21121556 is about 4595.8194046329. The cubic root of 21121556 is about 276.4237173030.

Adding to 21121556 its reverse (65512112), we get a palindrome (86633668).

The spelling of 21121556 in words is "twenty-one million, one hundred twenty-one thousand, five hundred fifty-six".