A073352 Positive integers making n^2*(n-1)*(2*n-1)^2*(7*n-1)/36 a square.

1, 4, 55, 868, 13825, 220324, 3511351, 55961284, 891869185, 14213945668, 226531261495, 3610286238244, 57538048550401, 916998490568164, 14614437800540215, 232914006318075268, 3712009663288664065

Offset: 0

Author

Michael Somos, Jul 27 2002

Keywords

• nonn

Examples

			G.f. = 1 + 4*x + 55*x^2 + 868*x^3 + 13825*x^4 + 220324*x^5 + 3511351*x^6 + ...
		

Links

• G. C. Greubel, Table of n, a(n) for n = 0..825
• Index entries for linear recurrences with constant coefficients, signature (17,-17,1).

Crossrefs

Cf. A007750, A077412.

Programs

GAP

a:=[1,4,55];; for n in [4..30] do a[n]:=17*a[n-1]-17*a[n-2]+a[n-3]; od; a; # G. C. Greubel, Feb 09 2020

Magma

I:=[1,4,55]; [n le 3 select I[n] else 17*Self(n-1) - 17*Self(n-2) + Self(n-3): n in [1..30]]; // G. C. Greubel, Feb 09 2020

Maple

seq( simplify((4 +3*ChebyshevU(n,8) -24*ChebyshevU(n-1,8))/7), n=0..30); # G. C. Greubel, Feb 09 2020

Mathematica

LinearRecurrence[{17,-17,1},{1,4,55},30] (* Harvey P. Dale, Dec 09 2018 *)

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}

Sage

[(4 +3*chebyshev_U(n,8) -24*chebyshev_U(n-1,8))/7 for n in (0..30)] # G. C. Greubel, Feb 09 2020

Formula

G.f.: (1 - 13*x + 4*x^2)/((1-x)*(1-16*x+x^2)).

a(n) = (4 + 3*ChebyshevU(n, 8) - 24*ChebyshevU(n-1, 8))/7. - G. C. Greubel, Feb 09 2020