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A253919
Indices of products of four distinct primes (A046386) in the sequence of products of 4 primes (A014613).
1
27, 44, 56, 63, 71, 78, 83, 99, 103, 111, 115, 130, 133, 139, 140, 145, 166, 168, 171, 176, 185, 188, 190, 199, 201, 207, 208, 213, 217, 221, 229, 233, 239, 244, 248, 266, 271, 274, 276, 278, 285, 292, 299, 306, 313, 316, 317, 320, 322, 325, 331, 337, 341, 347, 351, 353, 357, 363, 375, 381, 387, 388, 389, 393, 394, 396, 402
OFFSET
1,1
COMMENTS
Or, positions of squarefree numbers in A014613.
FORMULA
A014613(a(n))=A046386(n).
EXAMPLE
a(1) = 27 because A014613(27) = A046386(1) = 210 = 2*3*5*7 the first squarefree number in A014613.
a(10000) = 25632 because A014613(25632) = A046386(100000) = 135555 = 2*3*7*1291 10000st squarefree number in A014613.
MATHEMATICA
c = 0; s = {}; Do[If[4 == PrimeOmega[k], c++; If[{1, 1, 1, 1} == (#[[2]] & /@ FactorInteger[k]) , AppendTo[s, c]]], {k, 16, 3000}]; s
(* or *) c = 0; s2 = {}; Do[If[4 == PrimeOmega[k], c++; If[SquareFreeQ[k] , AppendTo[s2, c]]], {k, 16, 3000}]; s2
PROG
(PARI) {c = 0; for (k = 16, 3000, if (4 == bigomega (k), c++; if (issquarefree (k), print1 (c ", "))))}
CROSSREFS
Sequence in context: A306118 A114446 A141229 * A357077 A259504 A307373
KEYWORD
nonn
AUTHOR
Zak Seidov, Jan 19 2015
STATUS
approved