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

1,1

Comments

A number is an emirpimes if it is a semiprime and if its reverse is a different semiprime. Thus palindromic semiprimes are excluded.

Links

Table of n, a(n) for n=1..37.

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

Adjacent sequences: A375380 A375382 A375383 * A375386 A375388 A375389

Keyword

nonn,base,new

Author

Massimo Kofler, Aug 13 2024

Status

approved