21356661666256 has 20 divisors (see below), whose sum is σ = 47289750832672. Its totient is φ = 9152854999776.

The previous prime is 21356661666253. The next prime is 21356661666259. The reversal of 21356661666256 is 65266616665312.

It is an interprime number because it is at equal distance from previous prime (21356661666253) and next prime (21356661666259).

It is a super-2 number, since 2×21356661666256² (a number of 27 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21356661666194 and 21356661666203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21356661666251) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 95342239470 + ... + 95342239693.

Almost surely, 2^{21356661666256} is an apocalyptic number.

It is an amenable number.

21356661666256 is an abundant number, since it is smaller than the sum of its proper divisors (25933089166416).

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

21356661666256 is a wasteful number, since it uses less digits than its factorization.

21356661666256 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 190684479178 (or 190684479172 counting only the distinct ones).

The product of its digits is 83980800, while the sum is 61.

The spelling of 21356661666256 in words is "twenty-one trillion, three hundred fifty-six billion, six hundred sixty-one million, six hundred sixty-six thousand, two hundred fifty-six".