A217613 Absolute value of difference between the n-th "emirpimes" A097393(n) and its reversal.

36, 36, 54, 45, 36, 27, 36, 27, 54, 45, 396, 99, 198, 792, 198, 396, 693, 792, 792, 594, 693, 198, 396, 594, 99, 297, 99, 396, 297, 693, 99, 99, 594, 198, 297, 396, 594, 198, 594, 198, 198, 198, 99, 495, 99, 99, 297, 99, 297, 297, 396, 99, 198, 297

Offset: 1

Author

Jonathan Vos Post, Oct 08 2012

Keywords

• nonn
• base
• easy

Comments

An emirpimes ("semiprime" spelled backwards) is a semiprime whose (base 10) reversal is a different semiprime. The first such number is 15, because 15 reversed is 51 and both 15 and 51 are semiprimes (i.e., 15 = 3*5 and 51 = 3*17). Because of the decimal base, each value must be a multiple of 9.

Examples

			a(1) = absolute value of first emirpimes versus its reversal = |15 - 51| = |-36| = 36.
a(2) = |26 - 62| = |-36| = 36.
a(3) = |39 - 93| = |-54| = 54.
a(4) = |49 - 94| = |-45| = 45.
		

Links

• Post, Jonathan Vos, Emirpimes. From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein.

Crossrefs

Cf. A001358, A004086, A097393.

Programs

Mathematica

Abs[#-IntegerReverse[#]]&/@Select[Range[800],!PalindromeQ[#]&&PrimeOmega[ #] == PrimeOmega[IntegerReverse[#]]==2&] (* Harvey P. Dale, Mar 11 2023 *)

Formula

a(n) = |A097393(n) - R(A097393(n))| = |A097393(n) - A004086(A097393(n))|.