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.

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

Author

K. D. Bajpai, May 04 2014

Keywords

• nonn
• base
• less

Comments

All the terms in sequence are semiprimes (product of two primes) which are reversal of some square, ignoring leading zeros.

Examples

			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.
		

Links

• K. D. Bajpai, Table of n, a(n) for n = 1..360

Crossrefs

Cf. A001358, A115710, A115711.

Programs

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 *)