This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A273230 Squares that remain squares if you decrease them by 3 times a repunit with the same number of digits. 3
 4, 49, 529, 4489, 38809, 344569, 363609, 375769, 444889, 558009, 597529, 700569, 7198489, 35366809, 44448889, 65983129, 4444488889, 5587114009, 83574762649, 335330171929, 359763638809, 390241344249, 403831017529, 407200963129, 435775577689, 444444888889, 453557800089 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Apart from the initial term, any number ends in 9. LINKS Giovanni Resta, Table of n, a(n) for n = 1..10000 EXAMPLE 4 - 3*1 = 1 = 1^2; 49 - 3*11 = 16 = 4^2; 529 - 3*111 = 196 = 14^2. MAPLE P:=proc(q, h) local n; for n from 1 to q do if type(sqrt(n^2-h*(10^(ilog10(n^2)+1)-1)/9), integer) then print(n^2); fi; od; end: P(10^9, 3); MATHEMATICA sol[k_] := Block[{x, e = IntegerLength@k, d = Divisors@ k}, Union[ #+k/# & /@ Select[ Take[d, Ceiling[ Length@d/2]], EvenQ[x = #+k/#] && IntegerLength[ x^2/4] == e &]]^2/4]; r[n_] := 3 (10^n-1)/9; Flatten[sol /@ r /@ Range[12]] (* Giovanni Resta, May 18 2016 *) CROSSREFS Cf. A002275, A061844, A273229, A273231-A273234. Sequence in context: A053769 A173038 A198971 * A199028 A189146 A086094 Adjacent sequences:  A273227 A273228 A273229 * A273231 A273232 A273233 KEYWORD nonn,easy,base AUTHOR Paolo P. Lava, May 18 2016 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.