A165555 Primes obtained from other primes by prefixing a 5.

53, 523, 541, 547, 571, 5101, 5107, 5113, 5167, 5179, 5197, 5227, 5233, 5281, 5347, 5419, 5431, 5443, 5449, 5479, 5503, 5521, 5557, 5563, 5569, 5641, 5647, 5653, 5659, 5683, 5701, 5743, 5821, 5827, 5839, 5857, 5881, 5953, 51031, 51061, 51109, 51151, 51193, 51217

Offset: 1

Author

Parthasarathy Nambi, Sep 21 2009

Keywords

• base
• nonn

Comments

The primes are considered in increasing order. Primes with the same number of digits, the difference between adjacent terms seems to be a multiple of 3.

Examples

			5479 is a prime obtained by prefixing a 5 to the prime 479.
		

Links

• K. D. Bajpai, Table of n, a(n) for n = 1..10000
• Chris Caldwell, The First 10,000 Primes

Crossrefs

Cf. A000040, A165243, A165292, A165444.

Programs

Magma

[k : p in PrimesUpTo (2000) | IsPrime (k) where k is Seqint (Intseq (p) cat Intseq (5))]; // K. D. Bajpai, Jul 14 2017

Maple

A165555:= n-> (parse(cat(5,ithprime(n)))): select(isprime, [seq((A165555(n), n=1..1000))]); # K. D. Bajpai, Jul 14 2017

Mathematica

Select[Table[FromDigits[Join[IntegerDigits[5], IntegerDigits[Prime[n]]]], {n, 500}], PrimeQ] (*K. D. Bajpai, Jul 14 2017 *)
Select[5*10^IntegerLength[#]+#&/@Prime[Range[200]],PrimeQ] (* Harvey P. Dale, Sep 29 2024 *)

PARI

lista(nn) = forprime(p=2, nn, if (isprime(q=eval(concat(5, Str(p)))), print1(q, ", "))); \\ Michel Marcus, Jul 29 2017

Extensions

More terms from Vincenzo Librandi, Dec 02 2010

Missing term 5449 inserted by K. D. Bajpai, Jul 14 2017