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A266845 Primes p such that p+-2 and p+-4 are semiprimes. 2
53, 89, 449, 683, 1259, 4283, 6803, 11789, 12781, 13553, 16561, 18593, 18899, 20287, 29303, 35099, 36217, 37619, 52163, 54181, 64763, 65213, 67103, 103769, 115831, 116009, 125551, 126541, 147997, 154043, 155161, 155609, 166013, 173699, 181943, 188911, 190261, 196613 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..2500

EXAMPLE

a(1)=53 because 53 - 2 = 51 = 3*17, 53 + 2 = 55 = 5*11.

MAPLE

filter:= proc(n) andmap(t -> numtheory:-bigomega(t)=2, [n-4, n-2, n+2, n+4]) end proc:

select(filter, [seq(ithprime(i), i=1..20000)]); # Robert Israel, Aug 11 2019

MATHEMATICA

Select[Prime@ Range@ 18000, AllTrue[# + {-4, -2, 2, 4}, PrimeOmega@ # == 2 &] &] (* Michael De Vlieger, Jan 09 2016, Version 10 *)

PROG

(PARI) lista(nn) = {forprime(p=5, nn, if (bigomega(p-4)==2 && bigomega(p+4)==2 && bigomega(p-2)==2 && bigomega(p+2)==2, print1(p, ", ")); ); } \\ Michel Marcus, Jan 10 2016

(Magma) IsSemiprime:=func< p | &+[ k[2]: k in Factorization(p)] eq 2 >; [p: p in PrimesInInterval(3, 2*10^5)| IsSemiprime(p+2) and IsSemiprime(p+4)and IsSemiprime(p-2) and IsSemiprime(p-4)]; // Vincenzo Librandi, Jan 10 2016

CROSSREFS

Subsequence of A063643.

Sequence in context: A137869 A096697 A033234 * A238678 A142296 A180520

Adjacent sequences: A266842 A266843 A266844 * A266846 A266847 A266848

KEYWORD

nonn

AUTHOR

Zak Seidov, Jan 04 2016

STATUS

approved

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Last modified December 1 23:44 EST 2022. Contains 358485 sequences. (Running on oeis4.)