21256400406661 has 8 divisors (see below), whose sum is σ = 24293057229504. Its totient is φ = 18219750632160.

The previous prime is 21256400406649. The next prime is 21256400406737. The reversal of 21256400406661 is 16660400465212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21256400406661 - 2⁵ = 21256400406629 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21256400400661) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9493401 + ... + 11516833.

It is an arithmetic number, because the mean of its divisors is an integer number (3036632153688).

Almost surely, 2^{21256400406661} is an apocalyptic number.

It is an amenable number.

21256400406661 is a deficient number, since it is larger than the sum of its proper divisors (3036656822843).

21256400406661 is a wasteful number, since it uses less digits than its factorization.

21256400406661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3524171.

The product of its (nonzero) digits is 414720, while the sum is 43.

The spelling of 21256400406661 in words is "twenty-one trillion, two hundred fifty-six billion, four hundred million, four hundred six thousand, six hundred sixty-one".