21315988 has 6 divisors (see below), whose sum is σ = 37302986. Its totient is φ = 10657992.

The previous prime is 21315961. The next prime is 21315989. The reversal of 21315988 is 88951312.

It can be written as a sum of positive squares in only one way, i.e., 20088324 + 1227664 = 4482^2 + 1108^2 .

It is a super-2 number, since 2×21315988² = 908742688832288, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21315989) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2664495 + ... + 2664502.

Almost surely, 2^21315988 is an apocalyptic number.

It is an amenable number.

21315988 is a deficient number, since it is larger than the sum of its proper divisors (15986998).

21315988 is a wasteful number, since it uses less digits than its factorization.

21315988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5329001 (or 5328999 counting only the distinct ones).

The product of its digits is 17280, while the sum is 37.

The square root of 21315988 is about 4616.9240842795. The cubic root of 21315988 is about 277.2693232193.

The spelling of 21315988 in words is "twenty-one million, three hundred fifteen thousand, nine hundred eighty-eight".