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

1,1

Comments

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

Links

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

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

Cf. A001358, A115710, A115711.

Sequence in context: A077530 A115551 A227419 * A220972 A335088 A247009

Adjacent sequences: A242094 A242095 A242096 * A242098 A242099 A242100

Keyword

nonn,base,less

Author

K. D. Bajpai, May 04 2014

Status

approved