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A032662
a(n) is the least k such that k concatenated with k + n is prime.
4
1, 2, 1, 4, 3, 12, 1, 2, 1, 2, 3, 6, 1, 6, 3, 4, 5, 4, 5, 8, 7, 2, 21, 10, 17, 2, 1, 2, 3, 4, 1, 2, 7, 14, 3, 4, 1, 2, 1, 2, 11, 6, 5, 18, 3, 4, 3, 6, 1, 2, 1, 8, 5, 4, 7, 2, 1, 4, 5, 4, 11, 2, 1, 4, 3, 12, 1, 2, 9, 2, 3, 6, 1, 8, 9, 2, 3, 6, 1, 2, 1, 2, 5, 4, 929, 6, 3, 4, 5, 12, 1, 2, 1
OFFSET
0,2
COMMENTS
First terms of sequences '1', A030457, A032617-A032624, continued with displacements d > 9.
LINKS
EXAMPLE
a(22) = 21: the concatenation of 21 and 21 + 22 = 43 is 2143 and this is a prime.
MAPLE
tcat:= (a, b) -> a*10^(1+ilog10(b))+b:
f:= proc(n) local k;
for k from 1 + (n mod 2) by 2 do
if isprime(tcat(k, k+n)) then return k fi
od;
end proc:
map(f, [$0..100]); # Robert Israel, Sep 05 2024
CROSSREFS
Cf. A032663.
Sequence in context: A217927 A284709 A307365 * A185413 A138509 A099331
KEYWORD
nonn,base,look
AUTHOR
Patrick De Geest, May 15 1998
EXTENSIONS
Edited by Robert Israel, Sep 05 2024
STATUS
approved