21261668 has 6 divisors (see below), whose sum is σ = 37207926. Its totient is φ = 10630832.

The previous prime is 21261659. The next prime is 21261671. The reversal of 21261668 is 86616212.

It can be written as a sum of positive squares in only one way, i.e., 18852964 + 2408704 = 4342^2 + 1552^2 .

It is a super-2 number, since 2×21261668² = 904117052284448, which contains 22 as substring.

It is an unprimeable number.

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, 2657705 + ... + 2657712.

It is an arithmetic number, because the mean of its divisors is an integer number (6201321).

Almost surely, 2^21261668 is an apocalyptic number.

It is an amenable number.

21261668 is a deficient number, since it is larger than the sum of its proper divisors (15946258).

21261668 is a wasteful number, since it uses less digits than its factorization.

21261668 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5315421 (or 5315419 counting only the distinct ones).

The product of its digits is 6912, while the sum is 32.

The square root of 21261668 is about 4611.0376272592. The cubic root of 21261668 is about 277.0335990384.

The spelling of 21261668 in words is "twenty-one million, two hundred sixty-one thousand, six hundred sixty-eight".