21778660 has 12 divisors (see below), whose sum is σ = 45735228. Its totient is φ = 8711456.

The previous prime is 21778657. The next prime is 21778661. The reversal of 21778660 is 6687712.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 10381284 + 11397376 = 3222^2 + 3376^2 .

It is not an unprimeable number, because it can be changed into a prime (21778661) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 544447 + ... + 544486.

It is an arithmetic number, because the mean of its divisors is an integer number (3811269).

Almost surely, 2^21778660 is an apocalyptic number.

21778660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21778660 is an abundant number, since it is smaller than the sum of its proper divisors (23956568).

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

21778660 is a wasteful number, since it uses less digits than its factorization.

21778660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1088942 (or 1088940 counting only the distinct ones).

The product of its (nonzero) digits is 28224, while the sum is 37.

The square root of 21778660 is about 4666.7611895189. The cubic root of 21778660 is about 279.2610618137.

The spelling of 21778660 in words is "twenty-one million, seven hundred seventy-eight thousand, six hundred sixty".