Strobogrammatic number

[3] It is a type of ambigram, words and numbers that retain their meaning when viewed from a different perspective, such as palindromes.

[4] When written using standard characters (ASCII), the numbers, 0, 1, 8 are symmetrical around the horizontal axis, and 6 and 9 are the same as each other when rotated 180 degrees.

Although amateur aficionados of mathematics are quite interested in this concept, professional mathematicians generally are not.

For instance, in an ornate serif type, the numbers 2 and 7 may be rotations of each other; however, in a seven-segment display emulator, this correspondence is lost, but 2 and 5 are both symmetrical.

In duodecimal, the strobogrammatic numbers are (using inverted two and three for ten and eleven, respectively) Examples of strobogrammatic primes in duodecimal are: The most recent upside down year was 1961, or 2002 if the number 2 is included (in the case of seven-segment displays), and before that were sequentially 1881 and 1691, unless leading zeroes are allowed to be arbitrarily added.