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A264780 a(n) is the index of A246947(n) in A000977. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Is this a permutation of the positive integers?

LINKS

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

EXAMPLE

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.

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

PROG

(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); ); ); }

CROSSREFS

Cf. A000977, A246947, A264762.

Sequence in context: A105702 A184739 A081989 * A208276 A242487 A303592

Adjacent sequences:  A264777 A264778 A264779 * A264781 A264782 A264783

KEYWORD

nonn

AUTHOR

Michel Marcus, Nov 24 2015

STATUS

approved

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Last modified October 14 16:48 EDT 2019. Contains 328022 sequences. (Running on oeis4.)