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%I #37 Jul 21 2020 02:30:30
%S 20,26,55,68,171,258,310
%N Numbers m such that 7^m - 6^m is not squarefree, but 7^d - 6^d is squarefree for every proper divisor d of m.
%C Numbers m such that 7^m - 6^m is not squarefree not divisible by any smaller number of the same form.
%C 7^m - 6^m is nonsquarefree if and only if m is divisible by a term of this sequence. - _Jon E. Schoenfield_, Jan 01 2017
%C The smallest squares of 7^m - 6^m as defined above are 25, 169, 121, 289, 361, 1849, 961. - _Robert Price_, Mar 07 2017
%C a(8) >= 323. - _Jinyuan Wang_, May 15 2020
%C a(8) <= 381. 381, 406, 506, 610, 689, 979, 1027, 1081, 1332 are terms. - _Chai Wah Wu_, Jul 20 2020
%e 20 is in this sequence because 7^20 - 6^20 = 43242508113549025 is not squarefree but 7^d - 6^d is squarefree for every proper divisor d of 20 (i.e., for d = 1, 2, 4, 5, and 10): 7^1 - 6^1 = 1, 7^2 - 6^2 = 13, 7^4 - 6^4 = 1105, 7^5 - 6^5 = 13682, 7^10 - 6^10 = 222009013 are all squarefree.
%Y Cf. A016169, A237043, A280203, A280208, A280209, A280302.
%K nonn,more
%O 1,1
%A _Juri-Stepan Gerasimov_, Dec 31 2016
%E a(5)-a(7) from _Jinyuan Wang_, May 15 2020
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