A115711 -id:A115711 - cp's OEIS frontend

A115710 Semiprimes (A001358) whose digit reversal is a square.

4, 9, 10, 46, 94, 121, 169, 526, 961, 982, 1042, 1273, 1405, 1843, 4069, 4633, 5221, 6313, 6511, 6937, 9235, 9481, 9886, 10201, 10609, 12538, 12769, 14023, 16171, 16327, 16582, 16723, 18085, 18463, 18811, 40219, 42817, 42931, 44353, 44521

Offset: 1

Giovanni Resta, Jan 31 2006

			46=2*23 is semiprime and 64=8^2.

Cf. A001358, A115711.

Select[Range[50000],PrimeOmega[#]==2&&IntegerQ[Sqrt[FromDigits[ Reverse[ IntegerDigits[ #]]]]]&] (* Harvey P. Dale, Mar 03 2013 *)

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.

Original entry on oeis.org

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

K. D. Bajpai, May 04 2014

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

			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.

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

Cf. A001358, A115710, A115711.

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);

Select[IntegerReverse[Range[200]^2],PrimeOmega[#]==2&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 27 2018 *)

cp's OEIS Frontend

A115710 Semiprimes (A001358) whose digit reversal is a square.

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