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A272309 Lesser of two consecutive semiprimes with a prime difference. 4
4, 6, 22, 26, 35, 39, 46, 49, 55, 62, 69, 74, 77, 82, 91, 95, 106, 115, 119, 134, 143, 155, 159, 161, 166, 178, 183, 185, 187, 194, 203, 206, 215, 219, 221, 235, 247, 254, 259, 262, 265, 267, 287, 289, 295, 299, 303, 309, 314, 319, 321, 323, 327, 329, 339, 341, 355, 358, 362 (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

EXAMPLE

39 is in the sequence because 39 = 3*13, the next semiprime is 46 = 2*23, and 46-39 = 7 is prime.

MATHEMATICA

L=Select[Range@370, PrimeOmega@# == 2 &]; Pick[Most@L, PrimeQ@ Differences@ L] (* Giovanni Resta, Apr 25 2016 *)

PROG

(PARI) proxsem(n)=local(p, s, r); s=0; p=n; while(s==0, p+=1; if(bigomega(p)==2, s=1; r=p)); p

{for(i=1, 400, if(bigomega(i)==2, a=proxsem(i)-i; if(isprime(a), print1(i, ", "))))}

(PARI) list(lim)=my(v=List(), u=v); lim\=1; while(bigomega(lim++)!=2, ); forprime(p=2, lim\2, forprime(q=2, lim\p, listput(v, p*q))); v=Set(v); for(i=1, #v-1, if(isprime(v[i+1]-v[i]), listput(u, v[i]))); Set(u) \\ Charles R Greathouse IV, Apr 29 2016

CROSSREFS

Cf. A001358, A272306, A272307, A272308.

Sequence in context: A002270 A286358 A088228 * A108636 A101143 A083157

Adjacent sequences:  A272306 A272307 A272308 * A272310 A272311 A272312

KEYWORD

nonn

AUTHOR

Antonio Roldán, Apr 25 2016

STATUS

approved

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Last modified September 20 20:36 EDT 2018. Contains 315241 sequences. (Running on oeis4.)