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 A271105 Square 1000-gonal numbers (or square chiliagonal numbers): numbers that are square and chiliagonal (or 1000-gonal). 4
 1, 2504902401, 168859192076889601, 241636344867909601, 16289064572957666645861601, 1098070014289567941239426235218401, 1571330653655890087598658185258401, 105925731068562297456560368093353713060001, 7140610715067574113911463073574478824869628906401 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) is a number that is a square and a chiliagon. A chiliagon is a polygon with 1000 sides. Each a(n) ends with digit 1. The remainder of the division of a(n) by 5 is 1. The remainder of the division of a(n) by 9 is the periodic sequence: 1, 0, 4, 7, 0, 7, 4, 0, 1 of period 9. - Muniru A Asiru, Apr 10 2016 a(n) is odd since a(n) mod 10 = A000012(n). Since all odd numbers with one or two distinct prime factors are deficient, a(n) is deficient. E.g., 3844891281 = sigma(a(2)) < 2*a(2) = 5009804802. - Muniru A Asiru, Nov 17 2016 The digital root of a(n) is always 1, 4, 7 or 9. - Muniru A Asiru, Nov 29 2016 LINKS Colin Barker, Table of n, a(n) for n = 1..190 M. A. Asiru, All square chiliagonal numbers, Int J Math Edu Sci Technol, 47:7(2016), 1123-1134. Index entries for linear recurrences with constant coefficients, signature (1,0,6502873789598402,-6502873789598402,0,-1,1). FORMULA G.f.: x*(1 +2504902400*x +168859189571987200*x^2 +66274279001421598*x^3 +168859189571987200*x^4 +2504902400*x^5+x^6) / ((1 -x)*(1 -6502873789598402*x^3 +x^6)). - Colin Barker, Mar 31 2016 a(n) = A271470(n)*(499*A271470(n)-498). - Muniru A Asiru, Apr 10 2016 a(n) = (A271115(n))^2. - Muniru A Asiru, Apr 10 2016 EXAMPLE 2504902401 is in the sequence because 50049^2 = 2504902401 and the 2241th 1000-gonal number is 2504902401. - Colin Barker, Mar 31 2016 MATHEMATICA Rest@ CoefficientList[Series[x (1 + 2504902400 x + 168859189571987200 x^2 + 66274279001421598 x^3 + 168859189571987200 x^4 + 2504902400 x^5 + x^6)/((1 - x) (1 - 6502873789598402 x^3 + x^6)), {x, 0, 8}], x] (* Michael De Vlieger, Mar 31 2016 *) PROG (GAP) g:=1000; Q0:=(g-4)^2; D1:=2*g-4; S:=[ 2*[ 500, 1 ], 4*[ 1022201, 22880 ], 498*[ 8980, 201 ], 996*[ 1, 0 ], -2*[- 500, 1 ], -4*[- 1022201, 22880 ]];;      Length(S); S1:=Filtered(S, i->IsInt((i[1]+g-4)/(2*g-4)));; Length(S1);  #3 S2:=Filtered([1..Length(S)], i->IsInt((S[i][1]+g-4)/(2*g-4)));; Length(S2);  #3  [ 1, 3, 5 ] S3:=List(S2, i->S[i]);; Length(S3); #3 u:=40320199;;   v:=902490;;   G:=[[u, 2*(g-2)*v], [v, u]];; A:=List([1..Length(S3)], s->List(List([0..11], i->G^i*TransposedMat([S3[s]])), Concatenation));; Length(A); D1:=Union(List([1..Length(A)], k->A[k]));; Length(D1); D2:=List(D1, i-> [(i[1]+(g-4))/(2*(g-2)), i[2]/2] );; Length(D2); D3:=Filtered(D2, i->IsInt(i[1]));;  Length(D3); D4:=List(D3, i->i[2]^2);;  Length(D4); D5:=Set(D4);;  Length(D5); (PARI) Vec(x*(1 +2504902400*x +168859189571987200*x^2 +66274279001421598*x^3 +168859189571987200*x^4 +2504902400*x^5+x^6) / ((1 -x)*(1 -6502873789598402*x^3 +x^6)) + O(x^10)) \\ Colin Barker, Mar 31 2016 CROSSREFS Cf. A000290 (square), A195163 (1000-gonal). Sequence in context: A258611 A120290 A308377 * A134439 A288844 A028521 Adjacent sequences:  A271102 A271103 A271104 * A271106 A271107 A271108 KEYWORD nonn,easy AUTHOR Muniru A Asiru, Mar 30 2016 EXTENSIONS More terms from Colin Barker, Mar 31 2016 STATUS approved

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Last modified August 24 16:21 EDT 2019. Contains 326295 sequences. (Running on oeis4.)