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A181603 Twin primes ending in 1. 7
11, 31, 41, 61, 71, 101, 151, 181, 191, 241, 271, 281, 311, 421, 431, 461, 521, 571, 601, 641, 661, 811, 821, 881, 1021, 1031, 1051, 1061, 1091, 1151, 1231, 1291, 1301, 1321, 1451, 1481, 1621, 1721, 1871, 1931, 1951, 2081, 2111, 2131, 2141, 2311, 2341, 2381 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
These are twin primes == 1 (mod 30) or == 11 (mod 30) or == 21 (mod 30). In the first case they cannot be lower twin primes because the upper ones would be == 3 (mod 30) and divisible by 3. In the second case they cannot be upper twin primes because the lower ones would be == 9 (mod 30) and divisible by 3. The last case is excluded because that implies they are divisible by 3. In summary the upper twin primes in here are given by A282326, the lower twin primes in here by A282321. - R. J. Mathar, Feb 14 2017
LINKS
MAPLE
isA181603 := proc(p)
if isprime(p) and (isprime(p-2) or isprime(p+2)) then
if modp(p, 10) = 1 then
true;
else
false;
end if ;
else
false;
end if;
end proc:
for n from 1 to 1000 do
if isA181603(n) then
printf("%d, ", n) ;
end if;
end do: # R. J. Mathar, Feb 14 2017
MATHEMATICA
Select[Prime@ Range@ 360, Mod[ #, 10] == 1 && (PrimeQ[ # - 2] || PrimeQ[ # + 2]) &] (* Robert G. Wilson v, Nov 06 2010 *)
Select[Flatten[Select[Partition[Prime[Range[400]], 2, 1], #[[2]]-#[[1]] == 2&]], Mod[#, 10]==1&] (* Harvey P. Dale, Oct 24 2021 *)
CROSSREFS
Sequence in context: A040172 A040160 A040981 * A040983 A040979 A181182
KEYWORD
base,nonn
AUTHOR
Omar E. Pol, Nov 01 2010
EXTENSIONS
More terms from Robert G. Wilson v, Nov 06 2010
STATUS
approved

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Last modified February 25 10:32 EST 2024. Contains 370321 sequences. (Running on oeis4.)