21138256 has 10 divisors (see below), whose sum is σ = 40955402. Its totient is φ = 10569120.

The previous prime is 21138253. The next prime is 21138277. The reversal of 21138256 is 65283112.

It can be written as a sum of positive squares in only one way, i.e., 12138256 + 9000000 = 3484^2 + 3000^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21138251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 660555 + ... + 660586.

Almost surely, 2^21138256 is an apocalyptic number.

It is an amenable number.

21138256 is a deficient number, since it is larger than the sum of its proper divisors (19817146).

21138256 is a wasteful number, since it uses less digits than its factorization.

21138256 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1321149 (or 1321143 counting only the distinct ones).

The product of its digits is 2880, while the sum is 28.

The square root of 21138256 is about 4597.6359142498. The cubic root of 21138256 is about 276.4965506362.

The spelling of 21138256 in words is "twenty-one million, one hundred thirty-eight thousand, two hundred fifty-six".