Special odd numbers: Difference between revisions
Added Algol 68
(Added C# entry, cleaned up Ring entry (it wasn't producing all 194 results)) |
(Added Algol 68) |
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Odd numbers of the form p*q where p and q are distinct primes, where '''p*q < 1000'''
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=={{header|ALGOL 68}}==
<lang algol68>BEGIN # find some odd square free semi-primes #
# numbers of the form p*q where p =/= q and p, q are prime #
# reurns a list of primes up to n #
PROC prime list = ( INT n )[]INT:
BEGIN
# sieve the primes to n #
INT no = 0, yes = 1;
[ 1 : n ]INT p;
p[ 1 ] := no; p[ 2 ] := yes;
FOR i FROM 3 BY 2 TO n DO p[ i ] := yes OD;
FOR i FROM 4 BY 2 TO n DO p[ i ] := no OD;
FOR i FROM 3 BY 2 TO ENTIER sqrt( n ) DO
IF p[ i ] = yes THEN FOR s FROM i * i BY i + i TO n DO p[ s ] := no OD FI
OD;
# replace the sieve with a list #
INT p pos := 0;
FOR i TO n DO IF p[ i ] = yes THEN p[ p pos +:= 1 ] := i FI OD;
p[ 1 : p pos ]
END # prime list # ;
# show odd square free semi-primes up to 1000 #
INT max number = 1000;
[]INT prime = prime list( 100 * max number ); # (very) rough approximation of where the last prime under 1001 is #
[ 1 : max number ]BOOL numbers; FOR i TO max number DO numbers[ i ] := FALSE OD;
FOR i FROM 2 TO max number - 1 DO
FOR j FROM i + 1 TO max number
WHILE INT pq = prime[ i ] * prime[ j ];
pq < max number
DO
numbers[ pq ] := TRUE
OD
OD;
INT n count := 0;
FOR i TO max number DO
IF numbers[ i ] THEN
print( ( " ", whole( i, -4 ) ) );
n count +:= 1;
IF n count MOD 20 = 0 THEN print( ( newline ) ) FI
FI
OD
END</lang>
{{out}}
<pre>
15 21 33 35 39 51 55 57 65 69 77 85 87 91 93 95 111 115 119 123
129 133 141 143 145 155 159 161 177 183 185 187 201 203 205 209 213 215 217 219
221 235 237 247 249 253 259 265 267 287 291 295 299 301 303 305 309 319 321 323
327 329 335 339 341 355 365 371 377 381 391 393 395 403 407 411 413 415 417 427
437 445 447 451 453 469 471 473 481 485 489 493 497 501 505 511 515 517 519 527
533 535 537 543 545 551 553 559 565 573 579 581 583 589 591 597 611 623 629 633
635 649 655 667 669 671 679 681 685 687 689 695 697 699 703 707 713 717 721 723
731 737 745 749 753 755 763 767 771 779 781 785 789 791 793 799 803 807 813 815
817 831 835 843 849 851 865 869 871 879 889 893 895 899 901 905 913 917 921 923
933 939 943 949 951 955 959 965 973 979 985 989 993 995
</pre>
=={{header|C#|CSharp}}==
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