21686420 has 36 divisors (see below), whose sum is σ = 52979220. Its totient is φ = 7435008.

The previous prime is 21686419. The next prime is 21686443. The reversal of 21686420 is 2468612.

21686420 = T₃₆₉ + T₃₇₀ + ... + T₅₆₄.

It can be written as a sum of positive squares in 2 ways, for example, as 15476356 + 6210064 = 3934^2 + 2492^2 .

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10085 + ... + 12044.

It is an arithmetic number, because the mean of its divisors is an integer number (1471645).

Almost surely, 2^21686420 is an apocalyptic number.

21686420 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21686420 is an abundant number, since it is smaller than the sum of its proper divisors (31292800).

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

21686420 is a wasteful number, since it uses less digits than its factorization.

21686420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22152 (or 22143 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 29.

The square root of 21686420 is about 4656.8680462302. The cubic root of 21686420 is about 278.8662488448.

The spelling of 21686420 in words is "twenty-one million, six hundred eighty-six thousand, four hundred twenty".