Triangular numbers that are sandwiched between two semiprimes; or triangular numbers t such that t-1 and t+1 are both semiprime.

A121898

Triangular numbers that are sandwiched between two semiprimes; or triangular numbers t such that t-1 and t+1 are both semiprime.

Terms

    a(0) =120a(1) =300a(2) =528a(3) =780a(4) =2628a(5) =3240a(6) =3828a(7) =5460a(8) =13530a(9) =18528a(10) =19110a(11) =22578a(12) =25878a(13) =31878a(14) =32640a(15) =37128a(16) =49770a(17) =56280a(18) =64980a(19) =72390a(20) =73920a(21) =78210a(22) =103740a(23) =105570a(24) =115440a(25) =137550a(26) =159330a(27) =161028a(28) =277140a(29) =288420

External references