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A363352
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Triprimes that are the concatenation of a prime and a semiprime (in that order).
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1
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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
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OFFSET
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1,1
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COMMENTS
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If p is a prime and the number of digits of 3*p is in A363353, then the concatenation of p and 3*p is a term. The first term of this type is a(2728) = 37111.
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LINKS
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EXAMPLE
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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.
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MAPLE
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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));
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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