121021

Properties

Appears in sequences

• a(n) is the number of prime powers <= 3^n.at n=13A024623
• Erroneous version of A134996.at n=11A038136
• Non-palindromic primes which on subtracting their reversal give perfect squares.at n=30A080177
• Primes whose decimal representation also represents a prime in base 3.at n=21A089981
• Start with 100103 and repeatedly reverse the digits and add 2 to get the next term.at n=19A120218
• Dihedral calculator primes: p, p upside down, p in a mirror, p upside-down-and-in-a-mirror are all primes.at n=12A134996
• Number of planar n X n X n binary triangular grids symmetric both under 120 degree rotation and reflection with no more than 7 ones in any 5 X 5 X 5 subtriangle.at n=14A153958
• Greater of twin primes p such that 3*p-2 is also greater of twin primes.at n=34A177336
• Positions of prime powers p^e with p < e within A000961.at n=30A192187
• Palindromic primes in the sense of A007500 with digits '0', '1' and '2' only.at n=9A199302
• Emirps that become their own reversals when rotated through 180 degrees (including on calculator display).at n=31A209620
• Emirps (A006567) whose difference with the reversal is a perfect square.at n=13A217386
• Number of binary arrays indicating the locations of trailing edge maxima of a random length-n 0..3 array extended with zeros and convolved with 1,-2,1.at n=21A222148
• Bemirps that also interpret 2 and 5 as upside-down forms of each other, assuming a digital font.at n=13A335731
• Numbers k that are the representation of primes in base 3 and in base 4.at n=21A340290
• Concatenate the ternary strings for 1,2,...,n-1, n, n-1, ..., 2,1.at n=2A360504
• Prime numbersat n=11394