20978981 has 2 divisors, whose sum is σ = 20978982. Its totient is φ = 20978980.

The previous prime is 20978941. The next prime is 20978987. The reversal of 20978981 is 18987902.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17986081 + 2992900 = 4241^2 + 1730^2 .

It is a cyclic number.

It is not a de Polignac number, because 20978981 - 2⁶ = 20978917 is a prime.

It is a super-2 number, since 2×20978981² = 880235287596722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20978987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10489490 + 10489491.

It is an arithmetic number, because the mean of its divisors is an integer number (10489491).

Almost surely, 2^20978981 is an apocalyptic number.

It is an amenable number.

20978981 is a deficient number, since it is larger than the sum of its proper divisors (1).

20978981 is an equidigital number, since it uses as much as digits as its factorization.

20978981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 72576, while the sum is 44.

The square root of 20978981 is about 4580.2817598921. The cubic root of 20978981 is about 275.8003395660.

The spelling of 20978981 in words is "twenty million, nine hundred seventy-eight thousand, nine hundred eighty-one".