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A191474 Smallest prime q such that q + prime(n) is a power of 2. 2
2, 5, 3, 549755813881, 5, 3, 47, 13, 41, 3, 97, 2011, 23, 536870869, 17, 11, 5, 3, 61, 953, 439, 433, 173, 167, 31, 67108763, 409, 149, 19, 911, 140737488355201, 16253, 887, 373, 107, 2147483497, 32611, 349, 89, 83, 3917, 331, 16193, 2096959, 59, 313, 33554221 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Corresponding exponents of 2: 2, 3, 3, 39, 4, 4, 6, 5, 6, 5, 7, 11, 6, 29, 6, 6, 6, 6, 7, 10, 9, 9, 8, 8, 7, 1, 9, 8, 7, 10, 47, 14, 10, 9, 8, 31, 15, 9, 8, 8, 12, 9, 14, 21, 8, 9, 1, ...
LINKS
EXAMPLE
2 + 2 = 2^2,
3 + 5 = 2^3,
5 + 3 = 2^3,
7 + 549755813881 = 2^39,
11 + 5 = 2^4.
MAPLE
f:= proc(n) local p, m, t, q;
p:= ithprime(n);
for t from ilog2(p) do
q:= 2^t - p;
if isprime(q) then return q fi;
od;
end proc:
map(f, [$1..50]); # Robert Israel, Dec 23 2020
MATHEMATICA
f[p_] := NestWhile[2 # &, 2^Ceiling[Log[2, p]], ! PrimeQ[# - p] &] - p;
f /@ Prime@Range@47 (* David Trimas, Jul 30 2023 *)
CROSSREFS
Sequence in context: A239309 A077073 A307126 * A199602 A324057 A106315
KEYWORD
nonn
AUTHOR
Zak Seidov, Aug 28 2012
EXTENSIONS
a(26) corrected by Robert Israel, Dec 23 2020
STATUS
approved

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Last modified March 19 03:18 EDT 2024. Contains 370952 sequences. (Running on oeis4.)