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A324272
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a(n) = 2*13^(2*n).
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1
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2, 338, 57122, 9653618, 1631461442, 275716983698, 46596170244962, 7874752771398578, 1330833218366359682, 224910813903914786258, 38009927549761598877602, 6423677755909710210314738, 1085601540748741025543190722, 183466660386537233316799232018, 31005865605324792430539070211042
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OFFSET
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0,1
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COMMENTS
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x = A324271(n) and y = a(n) satisfy the Lebesgue-Ramanujan-Nagell equation x^2 + 7^(26*n+1) = 4*y^13 (see Theorem 2.1 in Chakraborty, Hoque and Sharma).
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LINKS
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FORMULA
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O.g.f.: 2/(1 - 169*x).
E.g.f.: 2*exp(169*x).
a(n) = 169*a(n-1) for n > 0.
a(n) = 2*169^n.
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EXAMPLE
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For A324271(0) = 181 and a(0) = 2, 181^2 + 7 = 32768 = 4*2^13.
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MAPLE
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a:=n->2*169^n: seq(a(n), n=0..20);
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MATHEMATICA
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2 169^Range[0, 20]
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PROG
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(GAP) List([0..20], n->2*169^n);
(Magma) [2*169^n: n in [0..20]];
(PARI) a(n) = 2*169^n;
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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