A264780 a(n) is the index of A246947(n) in A000977.

1, 3, 8, 13, 19, 26, 33, 2, 7, 14, 23, 43, 57, 67, 81, 93, 5, 18, 52, 72, 115, 138, 164, 10, 63, 127, 200, 240, 41, 49, 58, 66, 4, 16, 31, 47, 85, 107, 20, 60, 159, 214, 11, 34, 100, 134, 175, 22, 118, 234, 296, 75, 84, 6, 21, 39, 62, 109, 133, 27, 76, 197, 265

Offset: 1

Author

Michel Marcus, Nov 24 2015

Keywords

• nonn

Comments

Is this a permutation of the positive integers?

Examples

			The first 5 terms of A246947 are 30, 60, 90, 120, and 150, that is, the 1st, 3rd, 8th, 13th and 19th terms of A000977.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000977, A246947, A264762.

Programs

Maple

N:= 1000: # get all terms before the first term > N
W:= Vector(N, t -> if nops(numtheory:-factorset(t))<=2 then 0 else 1 fi):
WS:= ListTools:-PartialSums(convert(W, list)):
m:= 1:
F:= {2, 3,5}:
A[1]:= WS[30]:
W[30]:= 0:
for n from 2 do
    while W[m] = 0 and m < N do m:= m+1 od;
  for k from m to N do
     if W[k] = 1 and nops(numtheory:-factorset(k) intersect F) = 3 then
        A[n]:= WS[k];
        W[k]:= 0;
        F:= numtheory:-factorset(k);
        break
     fi
  od;
  if k > N then break fi;
od:
seq(A[i],i=1..n-1); # Robert Israel, Nov 26 2015

PARI

v246947(nn) = {a = 30; fa = (factor(a)[,1])~; va = [a]; vs = va; k = 0; while (k < nn, k = 1; while (!((#setintersect(fa, (factor(k)[,1])~) == 3) && (! vecsearch(vs, k))), k++); a = k; fa = (factor(a)[,1])~; va = concat(va, k); vs = vecsort(va);); va;}
v000977(nn) = {va = []; for (n=1, nn, if (omega(n) >= 3, va = concat(va, n));); va;}
lista(nn) = {v = v246947(nn); w = v000977(vecmax(v)); for (k=1, #v, for (j=1, #w, if (w[j] == v[k], print1(j, ", "); break);););}