A358894 a(n) is the smallest centered n-gonal number with exactly n distinct prime factors.
460, 99905, 463326, 808208947, 23089262218, 12442607161209225, 53780356630, 700326051644920151, 46634399568693102, 45573558879962759570353
Offset: 3
Examples
a(3) = 460, because 460 is a centered triangular number with 3 distinct prime factors {2, 5, 23} and this is the smallest such number.
Links
- Eric Weisstein's World of Mathematics, Centered Polygonal Number
- Eric Weisstein's World of Mathematics, Distinct Prime Factors
Programs
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PARI
a(n) = if(n<3, return()); for(k=1, oo, my(t=((n*k*(k+1))/2+1)); if(omega(t) == n, return(t))); \\ Daniel Suteu, Dec 05 2022
Extensions
a(8)-a(9) from Daniel Suteu, Dec 05 2022
a(10)-a(12) from Daniel Suteu, Dec 06 2022