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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
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
Sequence in context: A105702 A184739 A081989 * A208276 A242487 A335869
KEYWORD
nonn
AUTHOR
Michel Marcus, Nov 24 2015
STATUS
approved

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Last modified March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)