



2, 4, 8, 32, 64, 256, 512, 2048, 32768, 2097152, 1073741824, 549755813888, 1125899906842624, 9223372036854775808, 9671406556917033397649408, 39614081257132168796771975168, 633825300114114700748351602688
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OFFSET

1,1


COMMENTS

Indices k such that the number of toothpicks in the toothpick structure of A139250 after kth stage equals the nth Wagstaff prime A000979. All terms of this sequence are powers of 2 (see formulas).
For a picture of the nth Wagstaff prime as a toothpick structure see the Applegate link "A139250: the movie version", then enter N = a(n) and click "Update", for N = a(n) <= 32768 (due to the resolution of the movie).


LINKS



FORMULA



EXAMPLE

For n = 5 we have that a(5) = 64, then we can see that the number of toothpicks in the toothpick structure of A139250 after 64 stages is 2731 which coincides with the fifth Wagstaff prime, so we can write A139250(64) = A000979(5) = 2731. See the illustration in the ApplegatePolSloane paper, figure 3: T(64) = 2731 toothpicks.


MATHEMATICA

2^Reap[Do[If[PrimeQ[1+Sum[2^(2n1), {n, m}]], Sow[m]], {m, 100}]][[2, 1]] (* JeanFrançois Alcover, Oct 06 2018 *)


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



