OFFSET
1,2
COMMENTS
For values of a see A096031.
It is easier to generate the pairs sorted by b. A d-digit number b is a member iff 4*(10^(2*d)-10^d-b^2+b)+1 is a square. All such b occur twice, except for 1, which occurs once. There are no members with 2, 6, 7, or 8 digits. There are six distinct nine-digit members. - David Wasserman, May 15 2007
REFERENCES
J. S. Madachy, Madachy's Mathematical Recreations, pp. 166 Dover NY 1979.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..294
EXAMPLE
1726 of the sequence forms a pair with 150 and we indeed have T(150)+T(1726)=11325+1490401=1501726.
MATHEMATICA
f[n_] := Block[{k = n + 1, t1 = n(n + 1)/2, td = IntegerDigits[n]}, While[k < 15*n && t1 + k(k + 1)/2 != FromDigits[ Join[ td, IntegerDigits[k]]], k++ ]; If[k != 15*n, k, 0]]; Do[ k = f[n]; If[k != 0, Print[n, " & ", k]], {n, 10^6}] (* Robert G. Wilson v, Jun 21 2004 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Lekraj Beedassy, Jun 16 2004
EXTENSIONS
Two more terms from Robert G. Wilson v, Jun 21 2004
Terms from a(19) onwards from David Wasserman, May 15 2007
STATUS
approved