Multipling 21780000 by its sum of digits (18), we get a square (392040000 = 198002).
21780000 divided by its sum of digits (18) gives a square (1210000 = 11002).
Adding to 21780000 its reverse (8712), we get a palindrome (21788712).
Multipling 21780000 by its reverse (8712), we get a 4-th power (189747360000 = 6604).
21780000 divided by its reverse (8712) gives a square (2500 = 502).
It is an ABA number since it can be written as A⋅BA, here for A=2, B=3300.
Almost surely, 221780000 is an apocalyptic number.
21780000 is a gapful number since it is divisible by the number (20) formed by its first and last digit.
It is an amenable number.
It is a practical number, because each smaller number is the sum of distinct divisors of 21780000
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
21780000 is a wasteful number, since it uses less digits than its factorization.
21780000 is an odious number, because the sum of its binary digits is odd.
The square root of 21780000 is about 4666.9047558312. The cubic root of 21780000 is about 279.2667891656.
The spelling of 21780000 in words is "twenty-one million, seven hundred eighty thousand".