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A065891 The a(n)-th composite number is 2^n. 1
1, 3, 9, 20, 45, 96, 201, 414, 851, 1738, 3531, 7163, 14483, 29255, 58993, 118820, 239143, 480897, 966550, 1941540, 3898356, 7824444, 15699344, 31490742, 63151054, 126614174, 253804612, 508678161, 1019341795, 2042386082 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

COMMENTS

Index of n-th power of 2 in A002808.

Remainder of division 2^n/c[n] equals zero, where c[n]=A002808, the n-th composite.

Exponential increase with a factor >2 and approaching two.

LINKS

Table of n, a(n) for n=2..31.

EXAMPLE

n = 4, 16 is the 9th composite number: 4,6,8,9,10,12,14,15,16; a[4] = 9.

MATHEMATICA

Do[s=Mod[2^n, c[n]]; If[s==0, Print[n]], {n, 2, 1000000}]

Table[2^n-(PrimePi[2^n])-1, {n, 2, 31}]

CROSSREFS

Cf. A000079, A000720, A002808, A015910, A073800.

Sequence in context: A176163 A203861 A073801 * A321173 A147328 A220770

Adjacent sequences:  A065888 A065889 A065890 * A065892 A065893 A065894

KEYWORD

nonn

AUTHOR

Labos Elemer, Nov 28 2001

EXTENSIONS

Edited by Robert G. Wilson v, Jun 18 2002

STATUS

approved

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Last modified July 15 23:32 EDT 2020. Contains 335774 sequences. (Running on oeis4.)