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A272308 Lesser of two consecutive semiprimes such that their sum is prime. 4
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

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Last modified January 21 13:38 EST 2018. Contains 297994 sequences.