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The first 80 "super primes" (delete any single digit and the result is still a prime)
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| # see http://oeis.org/A051362 | |
| require "prime" | |
| def subprimes(number) | |
| digits = number.digits.reverse | |
| digits.collect.with_index do |d,idx| | |
| subset = digits.dup | |
| subset.delete_at(idx) | |
| subset.join.to_i.prime? | |
| end | |
| end | |
| def all_prime?(number) | |
| subprimes(number).inject(number.prime?) {|b,s| b && s} | |
| end | |
| puts Prime.lazy.select { |p| all_prime?(p) }. | |
| each.take(80).force |
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| 23 | |
| 37 | |
| 53 | |
| 73 | |
| 113 | |
| 131 | |
| 137 | |
| 173 | |
| 179 | |
| 197 | |
| 311 | |
| 317 | |
| 431 | |
| 617 | |
| 719 | |
| 1013 | |
| 1031 | |
| 1097 | |
| 1499 | |
| 1997 | |
| 2239 | |
| 2293 | |
| 3137 | |
| 4019 | |
| 4919 | |
| 6173 | |
| 7019 | |
| 7433 | |
| 9677 | |
| 10193 | |
| 10613 | |
| 11093 | |
| 19973 | |
| 23833 | |
| 26833 | |
| 30011 | |
| 37019 | |
| 40013 | |
| 47933 | |
| 73331 | |
| 74177 | |
| 90011 | |
| 91733 | |
| 93491 | |
| 94397 | |
| 111731 | |
| 166931 | |
| 333911 | |
| 355933 | |
| 477797 | |
| 477977 | |
| 633317 | |
| 633377 | |
| 665293 | |
| 700199 | |
| 719333 | |
| 746099 | |
| 779699 | |
| 901499 | |
| 901997 | |
| 944777 | |
| 962233 | |
| 991733 | |
| 1367777 | |
| 1440731 | |
| 1799999 | |
| 2668999 | |
| 3304331 | |
| 3716633 | |
| 4437011 | |
| 5600239 | |
| 6666437 | |
| 6913337 | |
| 7333331 | |
| 7364471 | |
| 7391117 | |
| 13334117 | |
| 22255999 | |
| 33771191 | |
| 38800999 |
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Could make the code faster by short-circuiting the loop in
subprimes(number)