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A375385
Triangular numbers that are emirpimes.
0
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
1,1
COMMENTS
A number is an emirpimes if it is a semiprime and if its reverse is a different semiprime. Thus palindromic semiprimes are excluded.
EXAMPLE
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.
MATHEMATICA
Select[Accumulate[Range[3200]], ! PalindromeQ[#] && PrimeOmega[#] == 2 && PrimeOmega[IntegerReverse[#]] == 2 &] (* Amiram Eldar, Aug 13 2024 *)
CROSSREFS
Intersection of A000217 and A097393.
Sequence in context: A070862 A077730 A110103 * A232305 A282946 A319623
KEYWORD
nonn,base
AUTHOR
Massimo Kofler, Aug 13 2024
STATUS
approved