A181931 - OEIS

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A181931

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

115, 205, 226, 289, 335, 497, 667, 718, 1027, 1057, 1079, 1135, 1141, 1154, 1195, 1234, 1243, 1247, 1286, 1315, 1322, 1343, 1357, 1379, 1387, 1402, 1415, 1466, 1469, 1502, 1513, 1514, 1538, 1658, 1679, 1691, 1703, 1765, 1769, 1774, 1817, 1843, 1882, 1927, 1937, 1942

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

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).

LINKS

Table of n, a(n) for n=1..46.

FORMULA

{a(n) = {k in A097393, k < R(k), such that A007953(k * R(k)) is prime} = {k in A097393 such that A007953(k * A004086(k)) is in A000040}.

EXAMPLE

The smallest emirpimes, 15, is not an element, because 15 * 51 = 765 and 7 + 6 + 5 = 18, which is composite.

a(1) = 115 because 115 * 511 = 58765 and 5+8+7+6+5 = 31 is prime.

a(2) = 205 because 205 * 502 = 102910 and 1+0+2+9+1+0 = 13 is prime.

a(3) = 226 because 226 * 622 = 140572 and 1+4+0+5+7+2 = 19 is prime.

MAPLE

read("transforms");

# insert A097393 code here

isA181931 := proc(n)

local R ;

R := digrev(n) ;

if n < R then

if isA097393(n) then

isprime(digsum(n*R)) ;

else

false;

end if;

else

false;

end if;

end proc:

for n from 1 to 2000 do

if isA181931(n) then

printf("%d, ", n) ;

end if;

end do: # R. J. Mathar, Apr 05 2012

CROSSREFS

Cf. A001358, A004086, A007953, A007954, A097393, A210547.

Sequence in context: A363790 A183626 A224673 * A229324 A277806 A122562

Adjacent sequences: A181928 A181929 A181930 * A181932 A181933 A181934

KEYWORD

nonn,base,easy

AUTHOR

Jonathan Vos Post, Apr 02 2012

EXTENSIONS

More terms from Robert G. Wilson v, Apr 04 2012

STATUS

approved