21356661612 has 96 divisors (see below), whose sum is σ = 58627457280. Its totient is φ = 5965390080.

The previous prime is 21356661563. The next prime is 21356661629. The reversal of 21356661612 is 21616665312.

It is a super-2 number, since 2×21356661612² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1249339 + ... + 1266317.

It is an arithmetic number, because the mean of its divisors is an integer number (610702680).

Almost surely, 2^21356661612 is an apocalyptic number.

21356661612 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21356661612, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29313728640).

21356661612 is an abundant number, since it is smaller than the sum of its proper divisors (37270795668).

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

21356661612 is a wasteful number, since it uses less digits than its factorization.

21356661612 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17743 (or 17741 counting only the distinct ones).

The product of its digits is 77760, while the sum is 39.

It can be divided in two parts, 2135666 and 1612, that added together give a triangular number (2137278 = T₂₀₆₇).

The spelling of 21356661612 in words is "twenty-one billion, three hundred fifty-six million, six hundred sixty-one thousand, six hundred twelve".