A272308 - OEIS

A272308

Lesser of two consecutive semiprimes whose sum is prime.

9, 14, 21, 22, 26, 33, 35, 62, 74, 82, 86, 115, 141, 155, 158, 226, 259, 267, 295, 326, 346, 358, 362, 393, 417, 453, 482, 623, 703, 718, 734, 771, 799, 914, 933, 934, 955, 995, 1011, 1041, 1043, 1142, 1154, 1174, 1195, 1286, 1294, 1346, 1363, 1401, 1438, 1522, 1538, 1603, 1655

(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

26 is in the sequence because 26 = 2*13, the next semiprime is 33 = 3*11, and 26+33 = 59 is prime.

MATHEMATICA

L = Select[Range@1660, PrimeOmega@# == 2 &]; Pick[Most@L, PrimeQ[Plus @@@ Partition[L, 2, 1]]] (* Giovanni Resta, Apr 25 2016 *)

PROG

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

for(i=1, 2000, 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, A272309.

Sequence in context: A006624 A184218 A272527 * A186778 A070552 A272141

Adjacent sequences: A272305 A272306 A272307 * A272309 A272310 A272311

KEYWORD

nonn

AUTHOR

Antonio Roldán, Apr 25 2016

STATUS

approved