login
A242097
Sp = reversal of some square s where s = x^2 for x = 1,2,.. (ignoring leading zeros). Sp is in the sequence if it is semiprime.
1
4, 9, 94, 46, 121, 961, 982, 4, 526, 9, 169, 6511, 5221, 9481, 1042, 6313, 4633, 1843, 1273, 94, 1405, 9235, 46, 9886, 6937, 4069, 10201, 61801, 94411, 18811, 121, 44521, 96721, 52231, 65431, 42931, 67351, 52651, 92161, 48361, 961, 16171, 98671, 65971, 96781
OFFSET
1,1
COMMENTS
All the terms in sequence are semiprimes (product of two primes) which are reversal of some square, ignoring leading zeros.
LINKS
EXAMPLE
a(3) = 94 = 2 * 47 which is semiprime. Reversing the digits gives 49 = 7^2.
a(4) = 46 = 2 * 23 which is semiprime. Reversing the digits gives 64 = 8^2.
MAPLE
with(StringTools): with(numtheory): A242097:= proc() local r; r:= parse(Reverse(convert(x^2, string))); if bigomega(r)=2 then RETURN (r); fi; end: seq(A242097 (), x=1..500);
MATHEMATICA
Select[IntegerReverse[Range[200]^2], PrimeOmega[#]==2&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 27 2018 *)
CROSSREFS
KEYWORD
nonn,base,less
AUTHOR
K. D. Bajpai, May 04 2014
STATUS
approved