Ormiston pairs: Difference between revisions

=={{header|J}}==

For this, we would like to be able to test if a prime number is the first value in an Ormiston pair:

<syntaxhighlight lang=J> isorm=: -:&(/:~)&":&> 4 p: ]</syntaxhighlight>

Then the task becomes:

<syntaxhighlight lang=J> (,. 4 p:]) p:30{.I. isorm i.&.(p:inv) 1e6

1913 1931

18379 18397

19013 19031

25013 25031

34613 34631

35617 35671

35879 35897

36979 36997

37379 37397

37813 37831

40013 40031

40213 40231

40639 40693

45613 45631

48091 48109

49279 49297

51613 51631

55313 55331

56179 56197

56713 56731

58613 58631

63079 63097

63179 63197

64091 64109

65479 65497

66413 66431

74779 74797

75913 75931

76213 76231

76579 76597

+/isorm i.&.(p:inv) 1e6 NB. number of Ormiston pairs less than 1e6

382

+/isorm i.&.(p:inv) 1e7 NB. number of Ormiston pairs less than 1e7

3722</syntaxhighlight>