21187970 has 16 divisors (see below), whose sum is σ = 38191608. Its totient is φ = 8463360.

The previous prime is 21187961. The next prime is 21187979. The reversal of 21187970 is 7978112.

It is an interprime number because it is at equal distance from previous prime (21187961) and next prime (21187979).

It can be written as a sum of positive squares in 4 ways, for example, as 7711729 + 13476241 = 2777^2 + 3671^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21187970.

It is not an unprimeable number, because it can be changed into a prime (21187979) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11300 + ... + 13040.

Almost surely, 2^21187970 is an apocalyptic number.

21187970 is a deficient number, since it is larger than the sum of its proper divisors (17003638).

21187970 is a wasteful number, since it uses less digits than its factorization.

21187970 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2965.

The product of its (nonzero) digits is 7056, while the sum is 35.

The square root of 21187970 is about 4603.0392133893. The cubic root of 21187970 is about 276.7131403681.

The spelling of 21187970 in words is "twenty-one million, one hundred eighty-seven thousand, nine hundred seventy".