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A335732
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Emirps whose concatenation of adjacent digit differences either form an emirp that also has this characteristic or form a single-digit prime, and whose emirp also has this characteristic.
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0
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13, 31, 79, 97, 347, 709, 743, 769, 907, 967, 1847, 7481
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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LINKS
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EXAMPLE
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7481 is in the list as the concatenation of adjacent digit differences forms an emirp (i.e., |7-4|=3; |4-8|=4; |8-1|=7; which form 347, which is an emirp as 743 is also prime). Furthermore, for 347, |3-4|=1; |4-7|=3; forms 13, which is an emirp as 31 is also prime. Finally, |1-3| = 2, which is prime. This characteristic is also true for the emirp of 7481 which is 1847 (i.e., 1847 forms 743 which forms 31 which finally forms 2).
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PROG
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(Python)
from sympy.ntheory import isprime as isp
i = []
for a in range(10, 1000000):
if isp(a):
b = str(a)
d=[]
for c in range(0, len(b)-1):
ee = abs(int(b[c])-int(b[c+1]))
d.append(str(ee))
f = ''.join(d)
g = b[::-1]
if isp(int(f)) and isp(int(g)):
if len(b)<3:
i.append(b)
else:
if f in i:
i.append(b)
print(', '.join(i))
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CROSSREFS
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KEYWORD
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base,nonn,fini,full,less
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AUTHOR
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STATUS
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approved
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