240331

Appears in sequences

• Quasi-Carmichael numbers to base -5: squarefree composites n such that prime p|n ==> p+5|n+5.at n=28A029565
• a(n) is the number of five element sets of distinct integer-sided trapezoids whose base angles are 60 degrees that fill an equilateral triangular grid of side n units.at n=35A391498