A307046 - OEIS

A307046

Numbers k such that k^2 reversed is a prime and k^2 + (k^2 reversed) is a semiprime.

4, 28, 40, 62, 106, 140, 193, 196, 274, 316, 334, 400, 410, 554, 556, 620, 862, 866, 874, 884, 962, 1004, 1025, 1066, 1154, 1174, 1190, 1205, 1256, 1274, 1294, 1360, 1390, 1394, 1396, 1400, 1744, 1784, 1816, 1844, 1891, 1900, 1927, 1960, 1981, 1988, 2672, 2696, 2710, 2722, 2740, 2786, 2800, 3016, 3026

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

OFFSET

1,1

LINKS

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

EXAMPLE

4^2=16, reversed is 61. 16+61=77 which is semiprime (7*11), so 4 is in this sequence.

MAPLE

revdigs:= proc(n) local L, i;

L:= convert(n, base, 10);

add(L[-i]*10^(i-1), i=1..nops(L))

end proc:

filter:= proc(n) local a, b;

a:= n^2;

b:= revdigs(a);

isprime(b) and numtheory:-bigomega(a+b)=2

end proc:

select(filter, [$1..10000]); # Robert Israel, Mar 31 2019

MATHEMATICA

Select[Range[50000],

PrimeQ[IntegerReverse[#^2]] &&

PrimeOmega[#^2 + IntegerReverse[#^2]] == 2 &]

CROSSREFS

Cf. A007488, A059007, A306301.

Sequence in context: A137314 A032405 A344467 * A179279 A061428 A069518

Adjacent sequences: A307043 A307044 A307045 * A307047 A307048 A307049

KEYWORD

nonn,base

AUTHOR

Robert Price, Mar 31 2019

STATUS

approved