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A218709
a(n) is smallest number such that a(n)^2 + 1 is divisible by 13^n.
11
0, 5, 70, 239, 239, 143044, 1999509, 6826318, 6826318, 822557039, 52199939826, 603633907222, 11356596271444, 11356596271444, 1828607235824962, 13920898306972194, 13920898306972194, 2675587335039691558, 49226908181248336040, 513050126578538629605
OFFSET
0,2
EXAMPLE
a(4) = 239 because 239^2+1 = 2*13^4.
MATHEMATICA
b=5; n13=13; jo=Join[{0, b}, Table[n13=13*n13; b=PowerMod[b, 13, n13]; b=Min[b, n13-b], {99}]]
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Nov 04 2012
STATUS
approved