21256561040 has 80 divisors (see below), whose sum is σ = 58061658816. Its totient is φ = 7135065600.

The previous prime is 21256561019. The next prime is 21256561057. The reversal of 21256561040 is 4016565212.

It is a tau number, because it is divible by the number of its divisors (80).

It is a junction number, because it is equal to n+sod(n) for n = 21256560988 and 21256561006.

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, 917606 + ... + 940485.

Almost surely, 2^21256561040 is an apocalyptic number.

21256561040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21256561040 is an abundant number, since it is smaller than the sum of its proper divisors (36805097776).

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

21256561040 is a wasteful number, since it uses less digits than its factorization.

21256561040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1858128 (or 1858122 counting only the distinct ones).

The product of its (nonzero) digits is 14400, while the sum is 32.

The spelling of 21256561040 in words is "twenty-one billion, two hundred fifty-six million, five hundred sixty-one thousand, forty".