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A246648 Numbers k such that 2*k + 1 divides 2^(k+1) - 1. 2
0, 1, 7, 127, 227, 647, 1351, 1907, 3239, 4607, 5219, 5975, 11447, 13159, 13919, 21527, 22049, 23759, 23939, 24839, 30959, 31283, 31583, 31967, 32767, 37223, 46091, 46511, 47267, 60479, 65663, 66527, 78539, 78599, 81727, 82799, 84311, 98405, 102671, 103967 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

These are the numbers k such that mean of the k-th row of the triangle at A027926 is an integer.  All such k except 0 and 1 are congruent to -1 mod 4.

LINKS

Table of n, a(n) for n=0..39.

EXAMPLE

The sum of the numbers row 7 of the triangular array at A027926 is 2^8 - 1 = 255, and the number of numbers in row 7 is 15, and 255/15 = 17; thus 7 is in this sequence, and 17 is in A246649.

MATHEMATICA

z = 140000; u = Select[Range[0, z], IntegerQ[(2^(# + 1) - 1)/(2 # + 1)] &]   (* A246648 *)

v = Table[(2^(u[[k]] + 1) - 1)/(2 u[[k]] + 1), {k, 1, 6}] (* A246649 *)

CROSSREFS

Cf. A246637, A246649.

Sequence in context: A202798 A204248 A084940 * A139987 A061744 A256146

Adjacent sequences:  A246645 A246646 A246647 * A246649 A246650 A246651

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Sep 01 2014

STATUS

approved

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Last modified February 19 07:51 EST 2019. Contains 320309 sequences. (Running on oeis4.)