A175251 - OEIS

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A175251

Composites (A002808) with nonprime (A018252) subscripts.

4

4, 9, 12, 15, 16, 18, 21, 24, 25, 26, 28, 32, 33, 34, 36, 38, 39, 40, 42, 45, 48, 49, 50, 51, 52, 55, 56, 57, 60, 63, 64, 65, 68, 69, 70, 72, 74, 76, 77, 78, 80, 81, 84, 86, 87, 88, 90, 91, 93, 94, 95, 98, 100

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

a(n) = composite(nonprime(n)) = A002808(A018252(n)). a(n) U A065858(n) = A002808(n), a(n+1) U A022449(n) = A002808(n) for n >= 1. a(1) = 4, a(n) = A050435(n-1) = composites (A002808) with composite (A002808) subscripts for n >=2.

LINKS

Table of n, a(n) for n=1..53.

EXAMPLE

a(5) = 16 because a(5) = c(b(5)) = c(9) = 16, c = composite, b = nonprime.

CROSSREFS

Sequence in context: A312849 A161544 A179395 * A368998 A287367 A312850

Adjacent sequences: A175248 A175249 A175250 * A175252 A175253 A175254

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Mar 13 2010

STATUS

approved