10	!
	!	REM ATN
	!
15	!
	!	KEYED IN BY TIMOTHY SHANE MCCOY
	!	AT CENTRAL STATE UNIVERSITY
	!	ON PDP 11/45
	!	VERSION RSTS/E  V06C
	!
20	INPUT X
30	S,A = 0
40	IF ABS(X) > 1
	THEN 300
50	FOR N = 1 TO 100
55	S1 = -S1
60	P = 1
70	FOR J = 1 TO 2*N-1
80	P = P * X
90	NEXT J
100	S = S + S1 * P/(2*N-1)
110	IF ABS(A-S) < 1E - 6
	THEN 400
120	A = S
130	NEXT N
140	GOTO 420
300	S = 1.570796326794897
310	S1 = 1
320	FOR N = 1 TO 100
325	S1 = -S1
330	P = 1
340	FOR J = 1 TO 2*N-1
350	P = P * X
360	NEXT J
370	S = S + S1/(P*(2*N-1))
380	IF ABS(S-A) < 1E-6
	THEN 400
385	A = S
390	NEXT N
395	GOTO 420
400	PRINT "DID CONVERGE"
410	GOTO 430
420	PRINT "DID NOT CONVERGE"
430	PRINT "SUM ="S,"ATN(X) ="ATN(X)
435	PRINT N
440	GOTO 10
500	END