A241764 Semiprimes sp such that sp-3 is also semiprime.

9, 25, 38, 49, 58, 65, 77, 85, 94, 118, 121, 122, 145, 146, 158, 161, 169, 205, 206, 209, 217, 218, 221, 262, 265, 298, 301, 302, 305, 326, 329, 358, 361, 365, 394, 398, 454, 469, 481, 485, 505, 514, 517, 529, 538, 545, 554, 562, 565, 586, 589, 614

Offset

1,1

Comments

Also semiprimes of the form 2^x - x.

The primes of the form 2^x - x are in A081296.

Links

K. D. Bajpai, Table of n, a(n) for n = 1..1100

Example

a(3)= 38 = 2*19, which is semiprime: 38-3 = 35 = 5*7 is also semiprime.
a(5)= 58 = 2*29, which is semiprime: 58-3 = 55 = 5*11 is also semiprime.

Maple

with(numtheory): A241764:= proc(); if bigomega(x)=2 and bigomega(x-3)=2 then RETURN (x); fi; end: seq(A241764 (), x=1..2000);

Mathematica

Flatten[Position[Partition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 700}], 4, 1], _?(First[ #] ==Last[#]==1&), {1}, Heads->False]]+3 (* Harvey P. Dale, Dec 21 2015 *)

Prog

(PARI) for(k=1, 500, if(bigomega(k)==2 && bigomega(k-3)==2, print1(k, ", "))) \\ Colin Barker, May 07 2014

Crossrefs

Cf. A001358, A092207, A123017, A198327.

Sequence in context: A226647 A147199 A147403 * A044451 A114057 A227518

Adjacent sequences: A241761 A241762 A241763 * A241765 A241766 A241767

Keyword

nonn

Author

K. D. Bajpai, Apr 29 2014

Status

approved