cp's OEIS Frontend

A rotationally ambigrammatic number (A045574) is one that can be rotated by 180 degrees resulting in a readable, most often new number. Such numbers, by definition, can only contain the digits 0, 1, 6, 8, 9.

If the number once rotated happens to be the same number (e.g., 6889) it is a strobogrammatic number. Those present here are the terms of A018848.

Numbers such as 100, which is a square with trailing zeros, have been excluded. Such numbers rotated by 180 degrees would be written with leading zeros. Typically this is not the way we write numbers.

This sequence is infinite as it contains (10^k + 3)^2 and (3*10^k + 1)^2 for any k >= 0 (note also that A004086((10^k + 3)^2) = (3*10^k + 1)^2 when k > 0). - Rémy Sigrist, Dec 30 2020

Primes which, upon subtracting one, give numbers which read the same upside-down. Not to be confused with strobogrammatic primes A007597 such as 181 or 619. Also, 263 is the largest known prime whose square is strobogrammatic. Not to be confused with strobogrammatic squares A018848 such as 109181601. After a(7) this sequence is exemplary, not complete (i.e. missing some values).

Nonpalindromic numbers which are invariant under a 180-degree rotation.

Numbers that are the same upside down and containing digits 6, 9.

Intersection of A000787 and A029742.

Union of this sequence and A006072 gives A000787.