3015021

Appears in sequences

• Number of Schur rings over Z_{7^n}.at n=9A270787
• a(n) = n^9 + 8*n^8 + 43*n^7 + 159*n^6 + 452*n^5 + 997*n^4 + 1725*n^3 + 2272*n^2 + 1990*n + 21.at n=4A270873