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A255675
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Least integer k such that the n-th prime of form m^2+1 divides the composite number k^2+1.
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0
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3, 3, 13, 31, 91, 183, 241, 381, 553, 651, 1261, 1561, 2863, 3081, 4291, 5403, 6973, 8011, 8743, 11991, 13341, 14281, 15253, 15751, 16771, 17823, 21171, 22351, 24181, 25441, 28731, 30801, 32221, 33673, 41413, 42231, 43891, 49953, 52671, 55461, 57361, 62251, 65281
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OFFSET
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1,1
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COMMENTS
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Consequence: this is a subsequence of A002061 (central polygonal numbers of the form m^2 - m + 1).
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LINKS
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FORMULA
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EXAMPLE
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a(3)=13 because A002496(3)=17, and 17 divides 13^2+1= 2*5*17.
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MAPLE
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with(numtheory):
nn:=1000:
for i from 1 to nn do:
p:=i^2+1:
if type(p, prime)=true
then
ii:=0:
for k from i+1 to 10^6 while(ii=0) do:
if irem(k^2+1, p)=0
then
ii:=1:printf(`%d, `, k):
else
fi:
od:
fi:
od:
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MATHEMATICA
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Clear[m]; m[1]=1; m[2]=2; m[n_] := m[n] = For[j = m[n-1]+2, True, j = j+2, If[PrimeQ[j^2+1], Return[j]]]; a[n_] := For[k = m[n]+1, True, k++, If[ Divisible[k^2+1, m[n]^2+1], Return[k]]]; Array[a, 50] (* Jean-François Alcover, Jul 21 2015 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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