Find squares n where n+1 is prime: Difference between revisions

Content deleted Content added

Inline

@@ Line 216: / Line 216: @@
 </pre>
+=={{header|Modula-2}}==
+<lang modula2>MODULE SquareAlmostPrime;
+FROM InOut IMPORT WriteCard, WriteLn;
+FROM MathLib IMPORT sqrt;
+CONST Max = 1000;
+VAR prime: ARRAY [0..Max] OF BOOLEAN;
+    i, sq: CARDINAL;
+PROCEDURE Sieve;
+    VAR i, j, sqmax: CARDINAL;
+BEGIN
+    sqmax := TRUNC(sqrt(FLOAT(Max)));
+    FOR i := 2 TO Max DO prime[i] := TRUE; END;
+    FOR i := 2 TO sqmax DO
+        IF prime[i] THEN
+            j := i * i;
+            WHILE j <= Max DO
+                prime[j] := FALSE;
+                j := j + i;
+            END;
+        END;
+    END;
+END Sieve;
+PROCEDURE isSquare(n: CARDINAL): BOOLEAN;
+    VAR sq: CARDINAL;
+BEGIN
+    sq := TRUNC(sqrt(FLOAT(n)));
+    RETURN sq * sq = n;
+END isSquare;
+BEGIN
+    Sieve;
+    FOR i := 2 TO Max DO
+        IF prime[i] THEN
+            sq := i-1;
+            IF isSquare(sq) THEN
+                WriteCard(sq, 4);
+                WriteLn;
+            END;
+        END;
+    END;
+END SquareAlmostPrime.</lang>
+{{out}}
+<pre>   1
+</pre>
 =={{header|PARI/GP}}==