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A122824 Prime(semiprime(n)) - semiprime(prime(n)). Commutator [A000040,A001358] at n. 12
1, 4, 9, 8, 10, 12, 24, 24, 32, 15, 46, 24, 27, 34, 25, 40, 44, 46, 51, 54, 53, 46, 54, 60, 70, 70, 98, 105, 104, 91, 64, 72, 45, 48, 95, 118, 120, 120, 116, 108, 100, 96, 101, 118, 102, 144, 123, 86, 76, 81, 136, 138, 143, 112, 132, 131, 153, 160, 171, 169 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A106349(n) - A106350(n).

EXAMPLE

a(1) = prime(semiprime(1)) - semiprime(prime(1)) = prime(4) - semiprime(2) = 7 - 6 = 1.

a(2) = prime(semiprime(2)) - semiprime(prime(2)) = prime(6) - semiprime(3) = 13 - 9 = 4.

a(3) = prime(semiprime(3)) - semiprime(prime(3)) = prime(9) - semiprime(5) = 23 - 14 = 9.

a(4) = prime(semiprime(4)) - semiprime(prime(4)) = prime(10) - semiprime(7) = 29 - 21 = 8.

MATHEMATICA

sp = Select[Range[1000], PrimeOmega[#] == 2 &]; Table[ Prime[ sp[[i]]] - sp[[Prime[i]]], {i, PrimePi@ Length@ sp}] (* Giovanni Resta, Jun 13 2016 *)

CROSSREFS

Cf. A000040, A001358, A106349, A106350.

Sequence in context: A019784 A276539 A011381 * A179396 A093491 A140808

Adjacent sequences:  A122821 A122822 A122823 * A122825 A122826 A122827

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Oct 23 2006

EXTENSIONS

a(33)-a(54) corrected by and a(55)-a(60) from Giovanni Resta, Jun 13 2016

STATUS

approved

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Last modified July 15 22:48 EDT 2019. Contains 325061 sequences. (Running on oeis4.)