OFFSET
1,1
COMMENTS
547 <= a(9) <= 689. 689, 732, 776, 903, 1055, 1081, 1332, 2525, 2628 are terms. - Chai Wah Wu, Jul 20 2020
EXAMPLE
10 is in this sequence because all 3^1 - 2^1 = 1, 3^2 - 2^2 = 5, 3^5 - 2^5 = 211 are squarefrees and 3^10 - 2^10 = 58025 = 5^2*2321 is not squarefree.
MATHEMATICA
Function[s, DeleteCases[#, 0] &@ MapIndexed[#1 Boole[Total@ Boole@ Map[Function[k, Divisible[#1, k]], Take[s, First@ #2 - 1]] == 0] &, s]]@ Select[Range@ 60, ! SquareFreeQ[3^# - 2^#] &] (* Michael De Vlieger, Dec 30 2016 *)
PROG
(PARI) is(n)=fordiv(n, d, if(!issquarefree(3^d-2^d), return(d==n))); 0 \\ Charles R Greathouse IV, Mar 01 2018
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Juri-Stepan Gerasimov and Charles R Greathouse IV, Dec 28 2016
STATUS
approved