A217591 Absolute differences between emirps (A006567) and their reversals.

18, 54, 18, 36, 54, 36, 18, 18, 594, 198, 792, 594, 594, 792, 792, 198, 396, 396, 594, 594, 594, 198, 396, 198, 396, 594, 594, 198, 198, 198, 792, 594, 198, 792, 594, 792, 7992, 180, 270, 2268, 540, 8532, 810, 6804, 1908, 7902, 360, 2358, 630, 2718, 180, 1908, 5904, 1998, 7992, 90, 6084, 8172, 8262, 8442

Offset: 1

Author

Jonathan Vos Post, Oct 07 2012

Keywords

• nonn
• base
• easy

Comments

This is unsorted, and in order of appearance of emirps.

All values are multiples of 18 (A008600). - Charles R Greathouse IV, Oct 15 2012

Examples

			a(1) = absolute value of first emirp versus its reversal = |13 - 31| = |-18| = 18.
a(2) = |17 - 71| = |-54| = 54.
a(3) = |31 - 13| = |18| = 18.
a(4) = |37 - 73| = |-36| = 36.
		

Crossrefs

Cf. A004086, A006567, A008600, A217286, A217386, A217387.

Programs

Maple

R:= n-> (s-> parse(cat(s[-i]$i=1..length(s))))(""||n):
q:= n-> isprime(n) and (p-> p<>n and isprime(p))(R(n)):
map(x-> abs(x-R(x)), select(q, [$2..1280]))[];  # Alois P. Heinz, Jul 12 2024

Formula

a(n) = | A006567(n) - R(A006567(n)) | = | A006567(n) - A004086(A006567(n)) |.

Extensions

Corrected and more terms from Georg Fischer, Jul 12 2024