
Curios:
Curios Search:
Participate: 
91 is pseudoprime to 35 bases less than 91. [Redman] 10^{n} + 91 {+ 0, + 2} are twin primes for n = 1, 2, 3 and 4. [Luhn] 91 is the smallest nontrivial odd composite (that is, its prime factors [7, 13] are not, at first glance, obvious). Every smaller odd composite is either a familiar square, ends in 5, has a digit sum that is a multiple of 3, or is obviously divisible by 11. 91 is the smallest pseudoprime satisfying the congruence 3^n = 3modn. Prime numbers that end with "91" occur more often than any other 2digit ending among the first ten million primes. [Gaydos]
(There are 2 curios for this number that have not yet been approved by an editor.)
Prime Curios! © 20002018 (all rights
reserved)
privacy statement
