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A275058 Primes p for which floor(p/10) is a perfect square. 1
11, 13, 17, 19, 41, 43, 47, 97, 163, 167, 251, 257, 367, 491, 499, 641, 643, 647, 811, 1009, 1213, 1217, 1447, 1693, 1697, 1699, 2251, 2897, 3613, 3617, 4001, 4003, 4007, 5297, 6257, 6761, 6763, 7297, 7841, 8419, 9001, 9007, 9613, 9619 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Terms are of the form 10*k^2 + t, with gcd(t, 10) = 1, i.e., {1, 3, 7, 9}.

Sum_{n>=1} 1/a(n) = 0.403068... converges.

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

EXAMPLE

For n=9, a(n)=163 is term because 16 left 3 is square 4^2=16.

For n=14, a(n)=491 is term because 49 left 1 is square 7^2=49.

MATHEMATICA

Select[Prime@ Range[5, PrimePi[10^4]], IntegerQ@ Sqrt@ Floor[#/10] &] (* or *)

Select[Union@ Flatten@ Map[10 Range[31]^2 + # &, {1, 3, 7, 9}], PrimeQ] (* Michael De Vlieger, Jul 14 2016 *)

PROG

(PARI) for(n=1, 1e3, forstep(p=10*n^2+1, 10*n^2+9, [2, 4, 2], if(isprime(p), print1(p", ")))) \\ Charles R Greathouse IV, Jul 15 2016

CROSSREFS

Cf. A226217.

Sequence in context: A068155 A271367 A226217 * A157175 A132244 A262731

Adjacent sequences:  A275055 A275056 A275057 * A275059 A275060 A275061

KEYWORD

nonn,base

AUTHOR

Dimitris Valianatos, Jul 14 2016

STATUS

approved

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Last modified August 2 12:30 EDT 2021. Contains 346424 sequences. (Running on oeis4.)