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A349168
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Numbers k such that sigma(k) and A003961(k) share a prime power divisor that is not a unitary divisor of A003961(k). Here A003961(n) is fully multiplicative function with a(prime(k)) = prime(k+1).
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4
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8, 20, 24, 27, 32, 40, 44, 54, 56, 60, 72, 80, 88, 92, 96, 100, 104, 108, 116, 120, 128, 132, 135, 140, 152, 160, 164, 168, 171, 176, 180, 184, 188, 189, 196, 200, 216, 224, 232, 236, 240, 248, 260, 261, 264, 270, 272, 276, 280, 288, 296, 297, 300, 308, 312, 320, 325, 328, 332, 342, 344, 348, 351, 352, 360, 368, 376
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OFFSET
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1,1
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COMMENTS
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Numbers k for which A349163(k) and A349164(k) are not relatively prime.
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LINKS
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EXAMPLE
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For n = 8 = 2^3, sigma(8) = 15 = 3*5, while A003961(8) = 3^3 = 27. These share the prime power divisor 3, which however is not a unitary divisor of 27, therefore 8 is included in this sequence.
For n = 32 = 2^5, sigma(32) = 63 = 3^2 * 7, while A003961(32) = 3^5 = 243. These share the prime power divisor 3^2, which however is not a unitary divisor of 243, therefore 32 is included.
For n = 40 = 2^3 * 5, sigma(40) = 90 = 2 * 3^2 * 5, while A003961(40) = 3^3 * 7 = 189. These share the prime power divisor 3^2, which however is not a unitary divisor of 189, therefore 40 is included.
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PROG
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(PARI)
A003961(n) = { my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); };
isA349168(n) = { my(u=A003961(n), x=gcd(u, sigma(n))); (1!=gcd(x, u/x)); };
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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