78420721531 has 2 divisors, whose sum is σ = 78420721532. Its totient is φ = 78420721530.

The previous prime is 78420721493. The next prime is 78420721583. The reversal of 78420721531 is 13512702487.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 78420721531 - 2¹⁷ = 78420590459 is a prime.

It is a super-2 number, since 2×78420721531² (a number of 23 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (78420727531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39210360765 + 39210360766.

It is an arithmetic number, because the mean of its divisors is an integer number (39210360766).

Almost surely, 2^78420721531 is an apocalyptic number.

78420721531 is a deficient number, since it is larger than the sum of its proper divisors (1).

78420721531 is an equidigital number, since it uses as much as digits as its factorization.

78420721531 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 94080, while the sum is 40.

The spelling of 78420721531 in words is "seventy-eight billion, four hundred twenty million, seven hundred twenty-one thousand, five hundred thirty-one".