181920

Appears in sequences

• Decimal concatenation of n, n+1, and n+2.at n=18A001703
• Concatenate the consecutive increasing numbers starting with Harshad(n) and ending with Harshad(n+1).at n=11A112131
• Duplicate of A001703.at n=18A127422
• List the positive integers but erase commas between terms if the digits just before and just after the comma have opposite parity.at n=5A367595