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%I #13 Aug 18 2024 11:44:23
%S 15,1891,3403,5671,12403,15931,64261,73153,104653,114481,188191,
%T 226801,286903,351541,371953,392941,497503,518671,597871,665281,
%U 703891,853471,933661,1034641,1104841,1159003,1309771,1537381,1660753,1755001,1987021,2077741,3022111,3270403,3913003,4142881,4567753
%N Triangular numbers that are emirpimes.
%C A number is an emirpimes if it is a semiprime and if its reverse is a different semiprime. Thus palindromic semiprimes are excluded.
%e 15 is the 5th triangular number. 15 = 3 * 5 and 51 = 3 * 17 are both semiprimes.
%e 1891 is the 61st triangular number. 1891 = 31 * 61 and 1981 = 7 * 283 are both semiprimes.
%e 3403 is the 82nd triangular number. 3403 = 41 * 83 and 3043 = 17 * 179 are both semiprimes.
%t Select[Accumulate[Range[3200]], ! PalindromeQ[#] && PrimeOmega[#] == 2 && PrimeOmega[IntegerReverse[#]] == 2 &] (* _Amiram Eldar_, Aug 13 2024 *)
%Y Intersection of A000217 and A097393.
%K nonn,base,new
%O 1,1
%A _Massimo Kofler_, Aug 13 2024
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