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A158724 Numbers n such that prime(n)^2 + 1 is a semiprime. 0
2, 3, 5, 8, 10, 17, 18, 20, 22, 26, 32, 34, 42, 46, 58, 70, 75, 80, 87, 89, 98, 104, 105, 115, 116, 121, 131, 133, 142, 152, 158, 167, 173, 175, 177, 180, 182, 189, 190, 193, 194, 218, 228, 232, 237, 239, 242, 267, 271, 280, 282, 291, 296, 326, 333, 337, 339, 347 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..58.

MATHEMATICA

lst={}; Do[If[Plus@@Last/@FactorInteger[Prime[n]^2+1]==2, AppendTo[lst, n]], {n, 0, 6!}]; lst

Select[Range[400], PrimeOmega[Prime[#]^2+1]==2&] (* Harvey P. Dale, Jun 14 2011 *)

PROG

(PARI) n=0; forprime(p=2, 1e4, n++; if(bigomega(p^2+1)==2, print1(n", "))) \\ Charles R Greathouse IV, Jun 14 2011

CROSSREFS

Sequence in context: A087279 A246346 A084907 * A289276 A181100 A036961

Adjacent sequences:  A158721 A158722 A158723 * A158725 A158726 A158727

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Mar 24 2009

STATUS

approved

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Last modified May 18 10:19 EDT 2021. Contains 343995 sequences. (Running on oeis4.)