A089186 -id:A089186 - cp's OEIS frontend

A094298 Numbers m such that m and its 10's complement are both semiprimes, i.e., m and 10^k - m, where k is the number of digits of m, are semiprime.

4, 6, 14, 15, 26, 35, 38, 49, 51, 62, 65, 74, 85, 86, 91, 94, 111, 121, 122, 129, 134, 158, 159, 169, 183, 185, 187, 201, 206, 209, 215, 219, 221, 237, 247, 254, 287, 301, 302, 303, 305, 319, 321, 326, 329, 365, 371, 377, 386, 403, 411, 417, 427, 446, 447, 458

Offset: 1

Jason Earls, Jun 02 2004

			201 is a term because both 201 and 1000 - 201 = 799 are semiprimes.

Robert Israel, Table of n, a(n) for n = 1..10000

Cf. A001358, A089186.

tc:= n -> 10^(1+ilog10(n))-n:
filter:= proc(n) numtheory:-bigomega(n)=2 and numtheory:-bigomega(tc(n))=2 end proc:
select(filter, [$1..1000]); # Robert Israel, Jul 02 2024

Select[Range[500],PrimeOmega[#]==PrimeOmega[10^IntegerLength[#]-#]==2&] (* Harvey P. Dale, Jan 17 2013 *)

A090671 Decreases from 10^k - 1 down to 1, restarting at 10^(k+1) - 1, for k >= 1.

Original entry on oeis.org

9, 8, 7, 6, 5, 4, 3, 2, 1, 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 89, 88, 87, 86, 85, 84, 83, 82, 81, 80, 79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63, 62, 61, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37

Offset: 1

Artemario Tadeu Medeiros da Silva (artemario(AT)uol.com.br), Dec 17 2003

Points of local maximum: ( 10^k - 1 ) k = {1,2,3,4,5,.....}

Cf. A089186, A035327.

cp's OEIS Frontend

A094298 Numbers m such that m and its 10's complement are both semiprimes, i.e., m and 10^k - m, where k is the number of digits of m, are semiprime.

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A090671 Decreases from 10^k - 1 down to 1, restarting at 10^(k+1) - 1, for k >= 1.

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