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A358864
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a(n) is the smallest n-gonal pyramidal number with exactly n distinct prime factors.
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6
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84, 1785, 299880, 1020510, 8897460, 102612510, 33367223274, 249417828660, 9177835927260, 10064864238489060, 5558913993302670, 15633689593760207970, 3792821921183752657200
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OFFSET
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3,1
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COMMENTS
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The corresponding indices of n-gonal pyramidal numbers are 7, 17, 84, 115, 220, 468, 3058, 5719, 18290, ...
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LINKS
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EXAMPLE
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a(3) = 84, because 84 is a tetrahedral (or triangular pyramidal) number with 3 distinct prime factors {2, 3, 7} and this is the smallest such number.
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PROG
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(PARI) a(n) = if(n<3, return()); for(k=1, oo, my(t=(k*(k+1)*((n-2)*k + (5-n)))\6); if(omega(t) == n, return(t))); \\ Daniel Suteu, Dec 05 2022
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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