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A073352
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Positive integers making n^2(n-1)(2n-1)^2(7n-1)/36 a square.
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2
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1, 4, 55, 868, 13825, 220324, 3511351, 55961284, 891869185, 14213945668, 226531261495, 3610286238244, 57538048550401, 916998490568164, 14614437800540215, 232914006318075268, 3712009663288664065
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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FORMULA
| G.f.: (1-13x+4x^2)/((1-x)(1-16x+x^2)). a(n)=16a(n-1)-a(n-2)-8. (Corrected by Paolo P. Lava (paoloplava(AT)gmail.com), Jun 19 2008)
a(n)=4/7+(3/14)*[8-3*sqrt(7)]^n+(3/14)*[8+3*sqrt(7)]^n, with n>=0 - Paolo P. Lava (paoloplava(AT)gmail.com), Jun 19 2008
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PROG
| (PARI) a(n)=if(n<0, a(-n), if(n<1, 1, 16*a(n-1)-a(n-2)-8)))
(PARI) a(n)=(4+3*real((8+3*quadgen(28))^n))/7
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CROSSREFS
| Cf. A007750.
Sequence in context: A151576 A204107 A202163 * A195634 A206384 A099122
Adjacent sequences: A073349 A073350 A073351 * A073353 A073354 A073355
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KEYWORD
| nonn
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AUTHOR
| Michael Somos, Jul 27 2002
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