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