A375385 Triangular numbers that are emirpimes.
15, 1891, 3403, 5671, 12403, 15931, 64261, 73153, 104653, 114481, 188191, 226801, 286903, 351541, 371953, 392941, 497503, 518671, 597871, 665281, 703891, 853471, 933661, 1034641, 1104841, 1159003, 1309771, 1537381, 1660753, 1755001, 1987021, 2077741, 3022111, 3270403, 3913003, 4142881, 4567753
Offset: 1
Examples
15 is the 5th triangular number. 15 = 3 * 5 and 51 = 3 * 17 are both semiprimes. 1891 is the 61st triangular number. 1891 = 31 * 61 and 1981 = 7 * 283 are both semiprimes. 3403 is the 82nd triangular number. 3403 = 41 * 83 and 3043 = 17 * 179 are both semiprimes.
Programs
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Mathematica
Select[Accumulate[Range[3200]], ! PalindromeQ[#] && PrimeOmega[#] == 2 && PrimeOmega[IntegerReverse[#]] == 2 &] (* Amiram Eldar, Aug 13 2024 *)
Comments