193131

Appears in sequences

• Triangular numbers with only odd digits.at n=27A117960
• Triangular numbers composed of digits {1,3,9}.at n=3A119121
• Triangular numbers t such that all the digits needed to write the consecutive triangular numbers from 0 to t fill exactly an equilateral triangle (no holes, no overlaps).at n=31A158030
• Triangular numbers k such that phi(k) is also a triangular number, where phi(k) is the Euler totient function (A000010).at n=5A287472
• Coefficients of non-constant terms of a Calabi-Yau modular form attached to 4-dimensional Dwork family.at n=1A300197
• Triangular numbers (A000217) in A353729.at n=11A370520