A101896
Primes obtained if 2^j for some suitable j is written backward.
Original entry on oeis.org
2, 61, 23, 821, 4201, 270131, 61277761, 274359834731, 23888027348153, 86936981079782063, 4243031147170261950811, 272838646828154727511151, 821882010875193363312928672952261, 274562423560500997742392394025368175422471, 4266472836315949449695828501889595072967427241
Offset: 1
Reverse 128, obtain 821, a prime.
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a:=Filtered(List(List([1..300],j->Reversed(ListOfDigits(2^j))),k->Sum([1..Size(k)],i->k[i]*10^(Size(k)-i))),IsPrime);; Print(a); # Muniru A Asiru, Dec 25 2018
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Select[FromDigits@ Reverse@ IntegerDigits[2^#] & /@ Range@ 3200, PrimeQ] (* Michael De Vlieger, Dec 03 2015 *)
A341713
Indices of Ennesrem primes: k such that A004094(k)-1 is prime.
Original entry on oeis.org
2, 3, 13, 21, 347, 1217, 1267, 16459, 100909, 342243
Offset: 1
13 is a term, since 2^13 = 8192 -> 2918 -> 2917, which is prime.
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for(n=1,10000,my(pe=fromdigits(Vecrev(digits(2^n)))-1);if(ispseudoprime(pe),print1(n,", "))) \\ Hugo Pfoertner, Feb 20 2021
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from sympy import isprime
def ok(k): return isprime(int(str(2**k)[::-1]) - 1)
for k in range(1, 2*10**3):
if ok(k): print(k, end=", ") # Michael S. Branicky, Feb 20 2021
A309607
Exponents k for which reversal(2^k-1) is prime.
Original entry on oeis.org
2, 3, 5, 53, 189, 293, 1107, 2181, 2695, 2871, 7667, 19999, 27471, 44537, 62323, 134367, 174295
Offset: 1
5 is included because for n=5, reversal(2^5-1)=13 is prime.
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Select[Range[7667], PrimeQ[IntegerReverse[2^# - 1]] &]
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isok(k) = isprime(fromdigits(Vecrev(digits(2^k-1)))); \\ Michel Marcus, Aug 10 2019
A318568
Primes p such that 2^p reversed is a prime.
Original entry on oeis.org
5, 7, 17, 37, 107, 137, 271
Offset: 1
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P0:=List(List([1..300],j->Reversed(ListOfDigits(2^j))),k->Sum([1..Size(k)],i->k[i]*10^(Size(k)-i)));;
a:=Filtered([1..Length(P0)],m->IsPrime(m) and IsPrime(P0[m]));; Print(a); # Muniru A Asiru, Dec 25 2018
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[p: p in PrimesUpTo(200) | IsPrime(Seqint(Reverse(Intseq(2^p))))];
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Select[Prime[Range[100]], PrimeQ[ToExpression[StringReverse[ToString[2^#]]]] &]
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isok(p) = isprime(p) && isprime(fromdigits(Vecrev(digits(2^p)))); \\ Michel Marcus, Sep 22 2018
A379938
Numbers k such that the k-th prime is a power of two reversed.
Original entry on oeis.org
1, 9, 18, 142, 575, 23652, 3633466, 10846595429, 802467018101, 2289255503212477
Offset: 1
The 9th prime is 23, 23 reversed is 32, and 32 = 2^5, so 9 is a term.
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import sympy
for (k, p) in enumerate(sympy.primerange(10**8)):
rev = int(str(p)[::-1])
# is rev a power of two (or zero)?
if rev & (rev - 1) == 0:
print(k + 1, end=",")
print()
A380992
Powers of two which produce a prime number when their digits are reversed.
Original entry on oeis.org
2, 16, 32, 128, 1024, 131072, 16777216, 137438953472, 35184372088832, 36028797018963968, 1180591620717411303424, 151115727451828646838272, 162259276829213363391578010288128, 174224571863520493293247799005065324265472, 1427247692705959881058285969449495136382746624
Offset: 1
The digits of 1024 (2^10) reverse to form the prime number 4201.
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