221681406 has 16 divisors (see below), whose sum is σ = 462639744. Its totient is φ = 70680984.

The previous prime is 221681357. The next prime is 221681407. The reversal of 221681406 is 604186122.

It is a super-2 number, since 2×221681406² = 98285291532273672, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (221681407) 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, 803056 + ... + 803331.

It is an arithmetic number, because the mean of its divisors is an integer number (28914984).

Almost surely, 2^221681406 is an apocalyptic number.

221681406 is an abundant number, since it is smaller than the sum of its proper divisors (240958338).

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

221681406 is a wasteful number, since it uses less digits than its factorization.

221681406 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1606415.

The product of its (nonzero) digits is 4608, while the sum is 30.

The square root of 221681406 is about 14888.9692725857. The cubic root of 221681406 is about 605.2151009839.

The spelling of 221681406 in words is "two hundred twenty-one million, six hundred eighty-one thousand, four hundred six".