1221221

Properties

Appears in sequences

• Primes that contain digits 1 and 2 only.at n=18A020450
• Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 1,2,2.at n=6A037551
• k th digit of a(n) = number of different digits within 2 places of k (not including k).at n=24A039987
• k th digit of a(n) is the number of different digits within 1 of k (not including k).at n=7A039988
• Erroneous version of A134998.at n=12A048662
• Palindromic primes with digit sum = 11.at n=4A070831
• Palindromic primes with middle digit 1.at n=8A082436
• Terms of A083393 such that the sum of the factorials of the digits is prime.at n=32A083394
• Palindromic primes p such that p+2 is also a prime: members of A083840 which are the smaller member of a twin prime pair.at n=31A083841
• Smallest palindromic prime containing exactly n 2's.at n=3A083973
• Smallest palindromic prime built using the palindromes with odd number of digits as central digits.at n=20A087364
• Palindromic primes p such that if each digit d is replaced by 10-d then the resulting palindrome is also a prime.at n=29A088092
• Palindromic primes that yield a prime when sandwiched between two 1's. (Prefixing and suffixing a 1 on both sides yields another palindromic prime.)at n=18A088269
• Palindromic primes that yield a prime when sandwiched between two 7's. (Prefixing and suffixing a 'seven' on both sides yields another pal prime).at n=28A088271
• Palindromic primes with both the number of digits and the digit sum also palindromic primes.at n=15A109830
• Palindromic primes in base 3 (written in base 3).at n=10A117698
• Palindromic primes in base 4 (written in base 4).at n=24A117699
• Palindromic primes in base 5 (written in base 5).at n=30A117700
• Dihedral palindromic primes.at n=13A134998
• Numbers such that each decimal digit d (for all d in the range 1 <= d <= 9) occurs only in runs of length exactly d.at n=30A140057