Empirical: a(n) = a(n-2) +a(n-3) +a(n-4) -a(n-7) -2*a(n-8) -2*a(n-9) -a(n-10) +2*a(n-12) +2*a(n-13) +2*a(n-14) +2*a(n-15) -a(n-17) -2*a(n-18) -2*a(n-19) -a(n-20) +a(n-23) +a(n-24) +a(n-25) -a(n-27)
Also a polynomial of degree 5 plus a linear quasipolynomial with period 420; the first 12 are :
Empirical for n mod 420 = 0: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58568/35)*n^2 - (60384/35)*n + 1
Empirical for n mod 420 = 1: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58358/35)*n^2 - (50934/35)*n + (27463/105)
Empirical for n mod 420 = 2: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58568/35)*n^2 - (57024/35)*n - (29047/105)
Empirical for n mod 420 = 3: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58358/35)*n^2 - (50934/35)*n - (9111/7)
Empirical for n mod 420 = 4: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58568/35)*n^2 - (60384/35)*n - (42551/105)
Empirical for n mod 420 = 5: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58358/35)*n^2 - (47574/35)*n - (5003/3)
Empirical for n mod 420 = 6: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58568/35)*n^2 - (60384/35)*n + (8651/35)
Empirical for n mod 420 = 7: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58358/35)*n^2 - (50934/35)*n - (15311/15)
Empirical for n mod 420 = 8: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58568/35)*n^2 - (57024/35)*n - (14435/21)
Empirical for n mod 420 = 9: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58358/35)*n^2 - (50934/35)*n - (24387/35)
Empirical for n mod 420 = 10: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58568/35)*n^2 - (60384/35)*n + (6365/21)
Empirical for n mod 420 = 11: a(n) = 2*n^5 + 75*n^4 - (1460/3)*n^3 + (58358/35)*n^2 - (47574/35)*n - (261217/105)
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