21051660 has 48 divisors (see below), whose sum is σ = 67366656. Its totient is φ = 4811712.

The previous prime is 21051643. The next prime is 21051673. The reversal of 21051660 is 6615012.

21051660 = T₂₄₄₉ + T₂₄₅₀ + ... + T₂₄₅₅.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 24642 + ... + 25481.

It is an arithmetic number, because the mean of its divisors is an integer number (1403472).

Almost surely, 2^21051660 is an apocalyptic number.

21051660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21051660 is an abundant number, since it is smaller than the sum of its proper divisors (46314996).

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

21051660 is a wasteful number, since it uses less digits than its factorization.

21051660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50142 (or 50140 counting only the distinct ones).

The product of its (nonzero) digits is 360, while the sum is 21.

The square root of 21051660 is about 4588.2088008285. The cubic root of 21051660 is about 276.1184641636.

Adding to 21051660 its reverse (6615012), we get a palindrome (27666672).

The spelling of 21051660 in words is "twenty-one million, fifty-one thousand, six hundred sixty".