Create sol.py

library/sol.py

@@ -0,0 +1,23 @@
+# http://oeis.org/A001333
+
+mat = [[0,0,1,0],[0,1,0,1],[1,0,2,0],[0,2,0,1]]
+mod = 10**9+7
+
+def matmult(mtx_a, mtx_b, mod):
+    tpos_b = zip( *mtx_b)
+    rtn = [[ sum( ea*eb for ea,eb in zip(a,b))%mod for b in tpos_b] for a in mtx_a]
+    return rtn
+
+def trace(A):
+    return sum(A[j][j] for j in range(len(A)))
+
+def matpow(A, p):
+    ret = A
+    for bit in bin(p)[3:]:
+        ret = matmult(ret, ret, mod)
+        if bit=='1':
+            ret = matmult(ret, A, mod)
+    return ret
+
+x = 2**10240+3
+print trace(matpow(mat, x))%mod