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A250293 Primes p such that p#+1 is a semiprime, where # is the primorial. 0
13, 19, 23, 43, 61, 67, 73, 83, 101, 139, 151, 173, 223, 251, 383 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

First unknown: 457.

LINKS

Table of n, a(n) for n=1..15.

Hisanori Mishima, Factorizations of many number sequences

EXAMPLE

a(1) = 13 so 13# + 1 = 30031 = 59 * 509 is a semiprime.

MATHEMATICA

Prime[#]&/@(Module[{pmrl=FoldList[Times, Prime[Range[50]]]}, Position[ pmrl, _?(PrimeOmega[ #+1]==2&)]]//Flatten) (* Harvey P. Dale, Apr 29 2017 *)

CROSSREFS

Cf. A005234, A006862, A078778.

Sequence in context: A121877 A109902 A214031 * A058898 A227092 A123840

Adjacent sequences:  A250290 A250291 A250292 * A250294 A250295 A250296

KEYWORD

nonn

AUTHOR

Eric Chen, Dec 24 2014

STATUS

approved

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Last modified December 10 12:22 EST 2019. Contains 329895 sequences. (Running on oeis4.)