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A110997
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Powers equal to (sum of first k primes) minus 1.
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2
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OFFSET
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1,2
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COMMENTS
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I have checked out to the first 250000 primes but the last entry is at the 504th prime, 3607.
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LINKS
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EXAMPLE
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128 is a term because 128 = -1 + Sum_{i=1..10} prime(i) = 2^7.
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MAPLE
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with(numtheory); egcd := proc(n) local L; L:=map(proc(z) z[2] end, ifactors(n)[2]); igcd(op(L)) end: s := proc(n) option remember; local p; if n=1 then [1, 2] else p:=ithprime(n); [n, s(n-1)[2]+p] fi end; t := proc(n) option remember; [n, s(n)[2]-1] end; PW:=[]; for z to 1 do for j from 1 to 250000 do if egcd(t(j)[2])>1 or t(j)[2]=1 then PW:=[op(PW), t(j)] fi od od; PW;
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MATHEMATICA
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s = 0; Do[s = s + Prime[n]; If[s == 2 || GCD @@ Transpose[ FactorInteger[s - 1]][[2]] > 1, Print[s - 1]], {n, 10^6}] (* Robert G. Wilson v, Oct 02 2005 *)
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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