A363352 Triprimes that are the concatenation of a prime and a semiprime (in that order).
76, 114, 116, 174, 222, 236, 238, 246, 255, 258, 282, 285, 286, 310, 316, 322, 325, 333, 338, 357, 369, 374, 385, 387, 434, 436, 474, 534, 539, 549, 555, 574, 582, 595, 596, 710, 715, 716, 722, 725, 762, 777, 782, 786, 795, 796, 834, 894, 1034, 1074, 1076, 1146, 1158, 1162, 1182, 1185, 1194, 1310
Offset: 1
Examples
a(3) = 116 is a term because 11 is a prime, 6 = 2*3 is a semiprime, and their concatenation 116 = 2^2 * 29 is a triprime.
Programs
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Maple
P[1]:= [2,3,5,7]: for d from 2 to 3 do P[d]:= select(isprime,[seq(i,i=10^(d-1)+1..10^d-1,2)]) od: for d from 1 to 3 do SP[d]:= select(t -> numtheory:-bigomega(t) = 2, [$10^(d-1).. 10^d-1]) od: R:= {}: for d from 2 to 4 do for d1 from 1 to d-1 do d2:= d-d1; V:= select(t -> numtheory:-bigomega(t)=3, {seq(seq(dcat(a,b),a=P[d1]),b=SP[d2])}); R:= R union V; od od: sort(convert(R,list));
Comments