A084632 Semiprimes such that when they are concatenated with their 10's complement, which also must be a semiprime, the result is a prime.

49, 91, 169, 237, 319, 321, 329, 377, 411, 417, 473, 529, 553, 583, 597, 629, 697, 713, 763, 779, 791, 817, 913, 923, 949, 1203, 1257, 1273, 1339, 1347, 1379, 1389, 1497, 1501, 1509, 1529, 1589, 1633, 1739, 1803, 1841, 1967, 1969, 2019, 2103, 2173, 2219

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

a(3)=169 because 169 is a semiprime and 1000-169 = 831 is a semiprime, while 169831 is a prime.

Mathematica

sctQ[n_]:=Module[{tc=10^IntegerLength[n]-n, j}, j=n*10^IntegerLength[ tc]+ tc; PrimeOmega[tc]==PrimeOmega[n]==2&&PrimeQ[j]]; Select[Range[ 2300], sctQ] (* Harvey P. Dale, Jan 02 2019 *)

Crossrefs

Cf. A001358.

Sequence in context: A320633 A108164 A020158 * A020176 A146064 A224905

Adjacent sequences: A084629 A084630 A084631 * A084633 A084634 A084635

Keyword

nonn,base

Author

Jason Earls, Jun 28 2003

Status

approved