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A242098 Numbers n such that the residue of n modulo floor(sqrt(n)) is prime. 1
11, 14, 18, 19, 22, 23, 27, 28, 32, 33, 38, 39, 41, 44, 45, 47, 51, 52, 54, 58, 59, 61, 66, 67, 69, 71, 74, 75, 77, 79, 83, 84, 86, 88, 92, 93, 95, 97, 102, 103, 105, 107, 112, 113, 115, 117, 123, 124, 126, 128, 134, 135, 137, 139, 146, 147, 149 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also, i^2+p(1), i^2+p(2),..., i^2+p(k), i^2+i+p(1), i^2+i+p(2),..., i^2+i+p(k), for i>=3, where p(n) is the n-th prime and p(k) is the largest prime strictly less than i.

LINKS

Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

EXAMPLE

floor(sqrt(28)) = 5. 28 modulo 5 = 3, which is prime, so 28 is in the sequence.

MATHEMATICA

Select[Range[200], PrimeQ[ Mod[#, Floor[Sqrt[#]]]]&] (* Harvey P. Dale, May 31 2019 *)

PROG

(Python)

from sympy import isprime

from math import sqrt, floor

from itertools import count

sequence=(_ in count(1) if isprime(_ % floor(sqrt(_))))

[next(sequence) for i in range(50)]

(PARI) for(n=1, 10^3, if(isprime(n%sqrtint(n)), print1(n", "))) \\ Jens Kruse Andersen, Aug 16 2014

CROSSREFS

Sequence in context: A084805 A159020 A015830 * A163672 A216580 A114948

Adjacent sequences:  A242095 A242096 A242097 * A242099 A242100 A242101

KEYWORD

nonn,easy

AUTHOR

Mark E. Shoulson, Aug 14 2014

EXTENSIONS

Added alternative formulation in comment.

STATUS

approved

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Last modified December 7 03:00 EST 2019. Contains 329836 sequences. (Running on oeis4.)