21061556 has 12 divisors (see below), whose sum is σ = 37084992. Its totient is φ = 10465848.

The previous prime is 21061541. The next prime is 21061591. The reversal of 21061556 is 65516012.

It is a super-2 number, since 2×21061556² = 887178282282272, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

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 in 3 ways as a sum of consecutive naturals, for example, 15500 + ... + 16803.

It is an arithmetic number, because the mean of its divisors is an integer number (3090416).

Almost surely, 2^21061556 is an apocalyptic number.

It is an amenable number.

21061556 is a deficient number, since it is larger than the sum of its proper divisors (16023436).

21061556 is a wasteful number, since it uses less digits than its factorization.

21061556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32470 (or 32468 counting only the distinct ones).

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21061556 is about 4589.2870906057. The cubic root of 21061556 is about 276.1617234644.

Adding to 21061556 its reverse (65516012), we get a palindrome (86577568).

The spelling of 21061556 in words is "twenty-one million, sixty-one thousand, five hundred fifty-six".