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A227942 Semiprimes formed by inserting a semiprime between the semiprime's ordered factors. 2
393, 2105, 2147, 3155, 5255, 5357, 25829, 26231, 28241, 29447, 33913, 35719, 39331, 56513, 58517, 59519, 79113, 210653, 212261, 214271, 215879, 216683, 219497, 314147, 315953, 317759, 318361, 320167, 321973, 323779, 326789, 329197, 520541, 523547, 529559, 530561 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Chris K. Caldwell and G. L. Honaker, Jr., Prime Curio for 13361

EXAMPLE

a(2)=2105 because the semiprime 10 inserted between its ordered prime factors (2 and 5) is a semiprime.

PROG

(PARI) issemi(n)=bigomega(n)==2

list(lim)=my(v=List(), t); forprime(q=2, sqrtint(lim\10), forprime(p=2, min(sqrtint(lim\q), q), t=eval(Str(p, p*q, q)); if(t>lim, next(2)); if(issemi(t), listput(v, t)))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Oct 04 2013

CROSSREFS

Cf. A001358, A229480, A227943.

Sequence in context: A158002 A083752 A047825 * A201815 A201554 A172636

Adjacent sequences:  A227939 A227940 A227941 * A227943 A227944 A227945

KEYWORD

nonn,base

AUTHOR

G. L. Honaker, Jr., Oct 03 2013

EXTENSIONS

More terms from Farideh Firoozbakht Oct 04 2013

STATUS

approved

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Last modified June 25 12:55 EDT 2019. Contains 324352 sequences. (Running on oeis4.)