cp's OEIS Frontend

A181931 Lesser of emirpimes pairs the product of whose members has prime digital sum.

%I A181931 #17 Feb 10 2025 20:46:13
%S A181931 115,205,226,289,335,497,667,718,1027,1057,1079,1135,1141,1154,1195,
%T A181931 1234,1243,1247,1286,1315,1322,1343,1357,1379,1387,1402,1415,1466,
%U A181931 1469,1502,1513,1514,1538,1658,1679,1691,1703,1765,1769,1774,1817,1843,1882,1927,1937,1942
%N A181931 Lesser of emirpimes pairs the product of whose members has prime digital sum.
%C A181931 This is to A210547 (Lesser of emirp pairs whose members have prime digital products) as emirpimes A097393 are to emirps A006567 and as A007953 (digital sums) are to A007954 (digital products).
%F A181931 {k in A097393, k < R(k), such that A007953(k * R(k)) is prime}, where R(k) = A004086(k).
%e A181931 The smallest emirpimes, 15, is not an element, because 15 * 51 = 765 and 7 + 6 + 5 = 18, which is composite.
%e A181931 a(1) = 115 because 115 * 511 = 58765 and 5+8+7+6+5 = 31 is prime.
%e A181931 a(2) = 205 because 205 * 502 = 102910 and 1+0+2+9+1+0 = 13 is prime.
%e A181931 a(3) = 226 because 226 * 622 = 140572 and 1+4+0+5+7+2 = 19 is prime.
%p A181931 read("transforms");
%p A181931 # insert A097393 code here
%p A181931 isA181931 := proc(n)
%p A181931     local R ;
%p A181931     R := digrev(n) ;
%p A181931     if n < R then
%p A181931         if isA097393(n) then
%p A181931             isprime(digsum(n*R)) ;
%p A181931         else
%p A181931             false;
%p A181931         end if;
%p A181931     else
%p A181931         false;
%p A181931     end if;
%p A181931 end proc:
%p A181931 for n from 1 to 2000 do
%p A181931     if isA181931(n) then
%p A181931         printf("%d,",n) ;
%p A181931     end if;
%p A181931 end do: # _R. J. Mathar_, Apr 05 2012
%Y A181931 Cf. A001358, A004086, A007953, A007954, A097393, A210547.
%K A181931 nonn,base,easy
%O A181931 1,1
%A A181931 _Jonathan Vos Post_, Apr 02 2012
%E A181931 More terms from _Robert G. Wilson v_, Apr 04 2012