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A307046
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Numbers k such that k^2 reversed is a prime and k^2 + (k^2 reversed) is a semiprime.
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2
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4, 28, 40, 62, 106, 140, 193, 196, 274, 316, 334, 400, 410, 554, 556, 620, 862, 866, 874, 884, 962, 1004, 1025, 1066, 1154, 1174, 1190, 1205, 1256, 1274, 1294, 1360, 1390, 1394, 1396, 1400, 1744, 1784, 1816, 1844, 1891, 1900, 1927, 1960, 1981, 1988, 2672, 2696, 2710, 2722, 2740, 2786, 2800, 3016, 3026
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OFFSET
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1,1
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LINKS
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EXAMPLE
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4^2=16, reversed is 61. 16+61=77 which is semiprime (7*11), so 4 is in this sequence.
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MAPLE
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revdigs:= proc(n) local L, i;
L:= convert(n, base, 10);
add(L[-i]*10^(i-1), i=1..nops(L))
end proc:
filter:= proc(n) local a, b;
a:= n^2;
b:= revdigs(a);
isprime(b) and numtheory:-bigomega(a+b)=2
end proc:
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MATHEMATICA
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Select[Range[50000],
PrimeQ[IntegerReverse[#^2]] &&
PrimeOmega[#^2 + IntegerReverse[#^2]] == 2 &]
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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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