1212121

Properties

Appears in sequences

• Primes that contain digits 1 and 2 only.at n=16A020450
• Two-bell analog of A028355.at n=9A028359
• Undulating primes (digits alternate).at n=47A032758
• Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 1,2.at n=6A037487
• Undulating palindromic primes of form ABABAB...BA with alternating prime and nonprime digits.at n=14A039944
• Smallest sets of 3 consecutive palindromic primes (palprimes) in arithmetic progression. The first prime of each set is listed.at n=9A059120
• Strictly undulating primes (digits alternate and differ by 1).at n=12A059170
• Undulating palindromic primes: numbers that are prime, palindromic in base 10, and the digits alternate: ababab... with a != b.at n=23A059758
• Palindromic primes with digit sum 10.at n=5A070250
• Catalan paths: numbers starting with 1 and ending with 1 where each digit is positive and adjacent digits differ by 1.at n=4A079215
• Palindromic primes with middle digit 2.at n=16A082438
• Palindromic prime units W appearing eight times in third-order fractal palindromic primes WvWxWvWmWvWxWvW, where parts WvWxWvW, WvW are also palindromic primes.at n=13A082600
• Palindromes p such that 5p + 1 is also a palindrome.at n=15A083833
• Palindromes n such that 6n + 1 is also a palindrome.at n=15A083835
• Palindromic primes p such that p-2 is also a prime: members of A083840 which are the larger member of a twin prime pair.at n=21A083842
• Smallest palindromic prime containing the n-th palindrome.at n=30A085054
• Smallest palindromic prime containing the n-th palindrome.at n=21A085054
• Palindromic primes with at least 3 digits in which the absolute difference of successive digits is identical.at n=27A085112
• Smallest palindromic prime built using the palindromes with odd number of digits as central digits.at n=11A087364
• a(n) = smallest prime of the form 10*K(n) + 1, where K is a number obtained by concatenation of n with itself, or 0 if no such prime exists.at n=11A087403