21047780 has 24 divisors (see below), whose sum is σ = 47600952. Its totient is φ = 7771392.

The previous prime is 21047777. The next prime is 21047813. The reversal of 21047780 is 8774012.

It can be written as a sum of positive squares in 4 ways, for example, as 16384 + 21031396 = 128^2 + 4586^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 40217 + ... + 40736.

It is an arithmetic number, because the mean of its divisors is an integer number (1983373).

Almost surely, 2^21047780 is an apocalyptic number.

21047780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21047780 is an abundant number, since it is smaller than the sum of its proper divisors (26553172).

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

21047780 is a wasteful number, since it uses less digits than its factorization.

21047780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80975 (or 80973 counting only the distinct ones).

The product of its (nonzero) digits is 3136, while the sum is 29.

The square root of 21047780 is about 4587.7859583900. The cubic root of 21047780 is about 276.1014994608.

The spelling of 21047780 in words is "twenty-one million, forty-seven thousand, seven hundred eighty".