A379693 a(n) is the least number k that has exactly n divisors <= sqrt(k) of the form 4*j+1.
1, 25, 90, 585, 1575, 2475, 5850, 9945, 16380, 20475, 36855, 45045, 69615, 122850, 135135, 176715, 218295, 225225, 495495, 405405, 348075, 696150, 675675, 765765, 1461915, 1351350, 2304225, 1576575, 4037670, 2027025, 2837835, 2297295, 4542615, 4594590, 5135130, 3828825, 6912675, 5360355, 8558550
Offset: 1
Keywords
Examples
a(3) = 90 because 90 has 3 divisors <= sqrt(90) of the form 4*j+1, namely 1, 5 and 9, and no smaller number works.
Programs
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Maple
N:= 90: # for a(0) .. a(N) f:= proc(n) nops(select(t -> t mod 4 = 1 and t^2 <= n, numtheory:-divisors(n))) end proc: V:= Array(0..N): count:= 0: for n from 1 while count < N+1 do v:= f(n); if v <= N and V[v] = 0 then V[v]:= n; count:= count+1 fi; od: convert(V, list);
Comments