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A100493
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a(n) = n + n-th semiprime.
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7
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5, 8, 12, 14, 19, 21, 28, 30, 34, 36, 44, 46, 48, 52, 54, 62, 66, 69, 74, 77, 79, 84, 88, 93, 99, 103, 109, 113, 115, 117, 122, 125, 127, 129, 141, 147, 152, 156, 158, 161, 163, 165, 172, 177, 179, 187, 189, 191, 194, 196, 206, 210, 212, 215, 221, 225, 234, 236
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OFFSET
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1,1
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COMMENTS
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This is the semiprime analog of A014688.
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LINKS
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Eric Weisstein, World of Mathematics, Semiprime.
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FORMULA
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EXAMPLE
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a(7) = 7 + semiprime(7) = 7 + 21 = 28.
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MAPLE
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N:= 1000: # to use semiprimes <= N
Primes:= select(isprime, [2, seq(i, i=3..N, 2)]):
Semiprimes:= sort(convert(select(`<=`, {seq(seq(Primes[i]*Primes[j], i=1..j), j=1..nops(Primes))}, N), list)):
seq(i+Semiprimes[i], i=1..nops(Semiprimes)); # Robert Israel, Dec 20 2015
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MATHEMATICA
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m=300;
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PROG
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(Magma)
m:=300;
A001222:=[n eq 1 select 0 else (&+[p[2]: p in Factorization(n)]): n in [1..4*m]];
(SageMath)
from sympy import primeomega
b=[n for n in (1..1000) if primeomega(n)==2]
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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