This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A027723 Palindromes of form k^2 + k + 7. 4
 7, 9, 313, 999, 31513, 75357, 78687, 90909, 98289, 3159513, 7642467, 9009009, 743080347, 900090009, 31413131413, 90000900009, 97474147479, 3105075705013, 9000009000009, 757082131280757, 900000090000009, 907340818043709, 90000000900000009, 92269201110296229 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS From Robert Israel, May 16 2018: (Start) Palindromes m such that 4*m - 27 is a square. Each term has an odd number of digits and ends in 3, 7 or 9. Contains 9*(1+10^k+10^(2*k)) for each k>=1. (End) LINKS Giovanni Resta, Table of n, a(n) for n = 1..45 P. De Geest, Palindromic Quasi_Over_Squares of the form n^2+(n+X) MAPLE R[1]:= [1, 3, 5, 7, 9]: X[1]:= R[1]: for k from 2 to 6 do   R[k]:= map(t -> seq(10^(k-1)*j+t, j=0..9), R[k-1]); X[k]:= map(t -> seq(j+10*t, j=0..9), X[k-1]) od: Res:= 7, 9: for k from 1 to 6 do   for j from 1 to 5*10^(k-1) do       r:= 10^(k+1)*X[k][j]+R[k][j];       for y from 0 to 9 do         if issqr(4*(r+10^k*y)-27) then           x:= r+10^k*y;           Res:= Res, x;         fi od od od: Res; # Robert Israel, May 16 2018 CROSSREFS Cf. A027722, A027692, A027756, A005471, A027721, A027725. Sequence in context: A012252 A262538 A306184 * A046265 A082705 A122577 Adjacent sequences:  A027720 A027721 A027722 * A027724 A027725 A027726 KEYWORD nonn,base AUTHOR EXTENSIONS More terms from Giovanni Resta, Aug 28 2018 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
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 8 18:37 EST 2019. Contains 329865 sequences. (Running on oeis4.)