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A327241
a(1) = 1. Thereafter, if n is prime, a(n) is the next prime after a(n-1), but written backwards in base 7; if n is composite, a(n) is the next composite after a(n-1), written backwards in base 7.
5
1, 2, 3, 4, 5, 6, 1, 4, 6, 8, 29, 18, 37, 26, 45, 34, 19, 44, 41, 6, 8, 15, 23, 24, 31, 32, 39, 40, 47, 48, 197, 102, 296, 153, 10, 36, 19, 44, 27, 4, 5, 6, 1, 4, 6, 8, 29, 18, 44, 27, 4, 6, 1, 4, 6, 8, 15, 16, 23, 24, 11, 36, 26, 45, 34, 5, 1, 4, 6, 8, 29, 18
OFFSET
1,2
COMMENTS
The sequence is written in base 10.
Rémy Sigrist's and Andrew Weimholt's methods from A326344 both show that a(n) <= 314, but the true maximum is 310. This can be shown by adapting Weimholt's argument to use values of n mod 30 rather than n mod 6.
LINKS
EXAMPLE
a(1) = 1 by definition. The next prime after a(6) = 6 is 7_10 = 10_7, so a(7) = 1_7 = 1_10 since 7 is prime.
MAPLE
A:= Vector(100):
A[1]:= 1:
for n from 2 to 100 do
if isprime(n) then
r:= nextprime(A[n-1])
else
for r from A[n-1]+1 while isprime(r) do od
fi;
A[n]:= revdigs(r)
od:
convert(A, list); # Robert Israel, Mar 23 2021
CROSSREFS
Sequence in context: A337223 A125934 A125935 * A316913 A319092 A243733
KEYWORD
base,nonn,look
AUTHOR
STATUS
approved