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A217591
Absolute differences between emirps (A006567) and their reversals.
0
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
1,1
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
FORMULA
a(n) = | A006567(n) - R(A006567(n)) | = | A006567(n) - A004086(A006567(n)) |.
EXAMPLE
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.
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
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Jonathan Vos Post, Oct 07 2012
EXTENSIONS
Corrected and more terms from Georg Fischer, Jul 12 2024
STATUS
approved

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Last modified September 20 13:29 EDT 2024. Contains 376072 sequences. (Running on oeis4.)