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A179338 Positive integers of the form (10*m^2+1)/11. 5
1, 91, 131, 401, 481, 931, 1051, 1681, 1841, 2651, 2851, 3841, 4081, 5251, 5531, 6881, 7201, 8731, 9091, 10801, 11201, 13091, 13531, 15601, 16081, 18331, 18851, 21281, 21841, 24451, 25051, 27841, 28481, 31451, 32131, 35281, 36001, 39331 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Here m=(11*(2*n-1)+7*(-1)^n)/4 for n>0.

LINKS

B. Berselli, Table of n, a(n) for n = 1..10000.

Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).

FORMULA

a(n) = (110*n*(n-1)+35*(2*n-1)*(-1)^n+39)/4.

G.f.: x*(1+90*x+38*x^2+90*x^3+1*x^4)/((1+x)^2*(1-x)^3).

a(n) = a(-n+1) = a(n-1)+2*a(n-2)-2*a(n-3)-a(n-4)+a(n-5).

MATHEMATICA

Select[(10Range[300]^2+1)/11, IntegerQ] (* or *) LinearRecurrence[ {1, 2, -2, -1, 1}, {1, 91, 131, 401, 481}, 50] (* Harvey P. Dale, Jul 10 2014 *)

PROG

(PARI) isok(n) = (((11*n-1) % 10 == 0) && issquare((11*n-1)/10)) \\ Michel Marcus, Jun 07 2013

(MAGMA) [(110*n*(n-1)+35*(2*n-1)*(-1)^n+39)/4: n in [1..50]]; // Vincenzo Librandi, Jul 10 2014

CROSSREFS

Cf. A113338, A179088, A179337, A179339, A179370.

Sequence in context: A020307 A020235 A046427 * A020238 A220171 A260974

Adjacent sequences:  A179335 A179336 A179337 * A179339 A179340 A179341

KEYWORD

nonn,easy

AUTHOR

Bruno Berselli, Jul 11 2010

STATUS

approved

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Last modified April 19 01:29 EDT 2019. Contains 322237 sequences. (Running on oeis4.)