645119

Appears in sequences

• a(1) = 1; then add 1, multiply by 2, subtract 3, multiply by 4, add 5, multiply by 6, subtract 7, multiply by 8 and so on.at n=15A085111
• a(n) = 2*(A056855(n)) /(phi(n)*n), where phi() is the Euler phi function.at n=23A099940
• a(n) = n!! - 1.at n=14A128882