21156780 has 48 divisors (see below), whose sum is σ = 61818624. Its totient is φ = 5396160.

The previous prime is 21156769. The next prime is 21156809. The reversal of 21156780 is 8765112.

It is a Smith number, since the sum of its digits (30) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (30).

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, 6286 + ... + 9045.

It is an arithmetic number, because the mean of its divisors is an integer number (1287888).

Almost surely, 2^21156780 is an apocalyptic number.

21156780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21156780 is an abundant number, since it is smaller than the sum of its proper divisors (40661844).

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

21156780 is a wasteful number, since it uses less digits than its factorization.

21156780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15366 (or 15364 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 30.

The square root of 21156780 is about 4599.6499866838. The cubic root of 21156780 is about 276.5772940792.

The spelling of 21156780 in words is "twenty-one million, one hundred fifty-six thousand, seven hundred eighty".