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A159754 Numbers n with property that n^2 ends with 81. 3
9, 41, 59, 91, 109, 141, 159, 191, 209, 241, 259, 291, 309, 341, 359, 391, 409, 441, 459, 491, 509, 541, 559, 591, 609, 641, 659, 691, 709, 741, 759, 791, 809, 841, 859, 891, 909, 941, 959, 991, 1009, 1041, 1059, 1091, 1109, 1141, 1159, 1191, 1209, 1241, 1259 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

First 9 terms = 9th row in A111445.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

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

FORMULA

a(1) = 9, a(2) = 41, a(n) = a(n-2)+50, n=3,4,...

a(n) = (1/2)*(50*n-25+7*(-1)^n), n=1,2,...

a(n) = a(n-1)+a(n-2)-a(n-3). G.f.: x*(9*x^2+32*x+9) / ((x-1)^2*(x+1)). - Colin Barker, Jul 04 2014

MAPLE

a:= n-> iquo(n-1, 2, 'r')*50 +[9, 41][r+1]:

seq(a(n), n=1..60);  # Alois P. Heinz, Dec 07 2016

MATHEMATICA

Select[Range[1300], PowerMod[#, 2, 100]==81&] (* or *) LinearRecurrence[{1, 1, -1}, {9, 41, 59}, 60] (* Harvey P. Dale, May 17 2018 *)

PROG

(PARI) select(n->n^2%100==81, vector(10^3, n, n)) \\ Colin Barker, Jul 04 2014

CROSSREFS

A159254 numbers n with property that n^2 ends with 49. A111445 n-th row contains first n numbers whose squares end in n^2.

Sequence in context: A093469 A120932 A034925 * A045804 A322055 A198943

Adjacent sequences:  A159751 A159752 A159753 * A159755 A159756 A159757

KEYWORD

nonn,base,easy

AUTHOR

Zak Seidov, Apr 21 2009

STATUS

approved

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Last modified June 25 17:47 EDT 2019. Contains 324353 sequences. (Running on oeis4.)