21256404 has 48 divisors (see below), whose sum is σ = 54048960. Its totient is φ = 6462720.

The previous prime is 21256399. The next prime is 21256447. The reversal of 21256404 is 40465212.

21256404 = T₃₉₇ + T₃₉₈ + ... + T₅₇₄.

It is a super-2 number, since 2×21256404² = 903669422022432, 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 15 ways as a sum of consecutive naturals, for example, 13119 + ... + 14649.

It is an arithmetic number, because the mean of its divisors is an integer number (1126020).

Almost surely, 2^21256404 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21256404, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27024480).

21256404 is an abundant number, since it is smaller than the sum of its proper divisors (32792556).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21256404 is a wasteful number, since it uses less digits than its factorization.

21256404 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1640 (or 1638 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 24.

The square root of 21256404 is about 4610.4667876474. The cubic root of 21256404 is about 277.0107343345.

It can be divided in two parts, 212 and 56404, that added together give a triangular number (56616 = T₃₃₆).

The spelling of 21256404 in words is "twenty-one million, two hundred fifty-six thousand, four hundred four".