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URL: https://oeis.org/A324669

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A324669
a(n) is the least k>0 such that A001359(n)+k^2 is in A001359.
1
6, 114, 162, 210, 24, 330, 6, 6, 18, 12, 30, 210, 6, 18, 120, 150, 330, 24, 6, 42, 30, 66, 96, 210, 180, 210, 42, 54, 60, 360, 6, 18, 630, 60, 210, 24, 30, 66, 24, 126, 30, 48, 1380, 24, 90, 102, 6, 30, 42, 18, 90, 90, 42, 54, 12, 36, 60, 186, 210, 12, 72, 24, 42, 24, 330, 60, 12
OFFSET
2,1
COMMENTS
Offset is 2 because 3+k^2 is never in A001359.
All terms are divisible by 6.
The generalized Bunyakovsky conjecture implies that a(n) always exists, for n >= 2.
a(n) = 6 if and only if A001359(n) is in A248367.
LINKS
EXAMPLE
a(3) = 114 because A001359(3)=11, 11+114^2=13007 is in A001359, and no smaller k works.
MAPLE
P:= select(isprime, {seq(i, i=3..10000, 2)}):
TP:= sort(convert(P intersect map(`-`, P, 2), list)):
f:= proc(p) local k;
for k from 6 by 6 do if isprime(p + k^2) and isprime(p + k^2 + 2) then return k fi od
end proc:
map(f, TP[2..-1]);
MATHEMATICA
With[{s = Select[Prime@ Range[3, 332], PrimeQ[# + 2] &]}, Array[Block[{k = 1}, While[! AllTrue[s[[#]] + k^2 + {0, 2}, PrimeQ], k++]; k] &, Length@ s]] (* Michael De Vlieger, Sep 03 2019 *)
CROSSREFS
Sequence in context: A288561 A291917 A066931 * A051228 A194132 A194476
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Sep 03 2019
STATUS
approved