19 lines
731 B
Text
19 lines
731 B
Text
An '''ultra-useful prime''' is a member of the sequence where each <span style="font-size:125%;">'''a(n)'''</span> is the smallest positive integer <span style="font-size:125%;">'''k'''</span> such that <span style="font-size:125%;">'''2<sup>(2<sup>n</sup>)</sup> - k'''</span> is prime.
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'''''k''' must always be an odd number since 2 to any power is always even.''
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;Task
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* Find and show here, on this page, the first '''10''' elements of the sequence.
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;Stretch
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* Find and show the next several elements. (The numbers get really big really fast. Only nineteen elements have been identified as of this writing.)
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;See also
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* [[oeis:A058220|OEIS:A058220 - Ultra-useful primes: smallest k such that 2^(2^n) - k is prime]]
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