Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #7 Sep 08 2022 08:45:30
%S 121,21952,343,484,5625,676,79507,8242408,9409
%N a(n) = smallest perfect power that begins and ends with digit n, 1 <= n <= 9; one-digit numbers are excluded.
%e a(8) = 202^3 = 8242408; there is no smaller perfect power that begins and ends with digit 8.
%o (Magma) PP:=[1] cat [ n: n in [2..9000000] | IsPower(n) ]; firstlast:=function(x); for n:=1 to #PP do k:=Intseq(PP[n], 10); if #k gt 1 and k[1] eq x and k[ #k] eq x then return PP[n]; end if; end for; return -1; end function; [ firstlast(d): d in [1..9] ]; // _Klaus Brockhaus_, Apr 16 2007
%Y Cf. A001597 (perfect powers), A075786 (palindromic perfect powers), A128827.
%K nonn,base,fini,full
%O 1,1
%A _J. M. Bergot_, Apr 12 2007
%E Edited, corrected and extended by _Klaus Brockhaus_, Apr 16 2007