A364452
Smallest k such that 4^(4^n) - k is prime.
Original entry on oeis.org
1, 5, 5, 159, 569, 1557, 2439, 25353, 24317, 164073
Offset: 0
a(2) = 5 because 4^(4^2) - 5 = 4294967291 is prime.
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lst={};Do[Do[p=4^(4^n)-k;If[PrimeQ[p],AppendTo[lst,k];Break[]],{k,2,11!}],{n,7}];lst
Table[k=1;Monitor[Parallelize[While[True,If[PrimeQ[4^(4^n)-k],Break[]];k++];k],k],{n,1,7}]
y[n_] := Module[{x = 4^(4^n)}, x - NextPrime[x, -1]]; Array[y, 7]
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a(n) = my(x = 4^(4^n)); x - precprime(x);
A364454
Smallest k such that 6^(6^n) - k is prime.
Original entry on oeis.org
1, 7, 35, 587, 629, 1819, 106843
Offset: 0
a(2) = 35 because 6^(6^2) - 35 = 10314424798490535546171949021 is prime.
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lst={};Do[Do[p=6^(6^n)-k;If[PrimeQ[p],AppendTo[lst,k];Break[]],{k,2,11!}],{n,7}];lst
Table[k=1;Monitor[Parallelize[While[True,If[PrimeQ[6^(6^n)-k],Break[]];k++];k],k],{n,1,7}]
y[n_] := Module[{x = 6^(6^n)}, x - NextPrime[x, -1]]; Array[y, 7]
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a(n) = my(x = 6^(6^n)); x - precprime(x);
A382666
Smallest k such that 7^(7^n) - k is prime.
Original entry on oeis.org
2, 2, 6, 512, 3918, 48966
Offset: 0
a(2) = 6 because 7^(7^2) - 6 = 256923577521058878088611477224235621321601 is prime.
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lst={};Do[Do[p=7^(7^n)-k;If[PrimeQ[p],AppendTo[lst,k];Break[]],{k,2,11!}],{n,7}];lst
Table[k=1;Monitor[Parallelize[While[True,If[PrimeQ[7^(7^n)-k],Break[]];k++];k],k],{n,0,7}]
y[n_] := Module[{x = 7^(7^n)}, x - NextPrime[x, -1]]; Array[y, 7]
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a(n) = my(x = 7^(7^n)); x - precprime(x-1);
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from sympy import prevprime
def a(n):
base = 7**(7**n)
return base - prevprime(base)
# Jakub Buczak, May 04 2025
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