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A048640 Binary encoding of the squarefree numbers, A005117. 4
1, 2, 4, 8, 6, 16, 10, 32, 64, 18, 12, 128, 256, 20, 34, 512, 66, 1024, 14, 2048, 36, 130, 24, 4096, 258, 68, 8192, 22, 16384, 514, 32768, 132, 65536, 40, 260, 1026, 131072, 262144, 2050, 72, 38, 524288, 516, 26, 1048576, 2097152, 4098, 48, 70, 4194304 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = 2^i1+2^i2+...+2^iz, where A005117(n) = p_i1*p_i2*p_i3*...*p_iz (p_i stands for the i-th prime, where the first prime is 2).

EXAMPLE

10 = 2*5 = p_1*p_3 -> 2^1+2^3 = 2+8 = 10.

MATHEMATICA

Total[2^PrimePi@ # &@ Map[First, FactorInteger@ #]] & /@ Select[Range@ 80, SquareFreeQ] (* Michael De Vlieger, Oct 01 2015 *)

PROG

(PARI) lista(nn) = {for (n=1, nn, if (issquarefree(n), if (n==1, x = n, f = factor(n); x = sum(k=1, #f~, 2^primepi(f[k, 1]))); print1(x, ", "); ); ); } \\ Michel Marcus, Oct 01 2015

CROSSREFS

Cf. A048639.

Sequence in context: A253886 A253885 A140692 * A242353 A277331 A124510

Adjacent sequences:  A048637 A048638 A048639 * A048641 A048642 A048643

KEYWORD

nonn

AUTHOR

Antti Karttunen, Jul 14 1999

STATUS

approved

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Last modified February 18 05:40 EST 2019. Contains 320245 sequences. (Running on oeis4.)