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A215420 Primes that remain prime when a single digit 7 is inserted between any two consecutive digits or as the leading or trailing digit. 12
3, 19, 97, 433, 487, 541, 691, 757, 853, 1471, 2617, 2953, 4507, 6481, 7351, 7417, 8317, 13177, 31957, 42457, 46477, 47977, 50077, 59053, 71917, 73897, 74377, 77479, 77743, 77761, 79039, 99103, 175687, 220897, 271177, 360973 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..63 (all terms up to and including the 1 millionth prime)
EXAMPLE
59053 is prime as are 590537, 590573, 590753, 597053, 579053, and 759053.
MAPLE
A215420:=proc(q, x)
local a, b, c, d, i, n, ok;
for n from 1 to q do
a:=ithprime(n); b:=0; while a>0 do b:=b+1; a:=trunc(a/10); od;
a:=ithprime(n); ok:=1;
for i from 0 to b do
c:=a+9*10^i*trunc(a/10^i)+10^i*x; if not isprime(c) then ok:=0; break; fi;
od;
if ok=1 then print(ithprime(n)); fi;
od; end:
A215420(1000, 7);
MATHEMATICA
Select[Prime[Range[31000]], AllTrue[FromDigits/@Table[Insert[ IntegerDigits[ #], 7, n], {n, IntegerLength[#]+1}], PrimeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Oct 29 2020 *)
CROSSREFS
Sequence in context: A049153 A074361 A126187 * A303542 A294251 A294392
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava, Aug 10 2012
STATUS
approved

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Last modified June 25 18:50 EDT 2024. Contains 373707 sequences. (Running on oeis4.)