login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A179634 Primes p such that p + d and p-d are primes, where d is the sum of floors of square roots of the digits of p. 1
5, 593, 647, 1097, 1187, 1367, 1453, 1663, 1753, 1783, 1873, 1907, 2287, 2377, 2417, 2683, 3463, 3637, 3923, 4513, 5413, 5807, 6263, 6317, 6373, 7523, 7823, 8087, 8117, 8237, 8713, 10853, 11807, 11833, 11903, 15313, 15803, 16063, 16223, 17027, 18223 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..2000

EXAMPLE

a(3)=647 since 647+[int(sqrt(6))+int(sqrt(4))+int(sqrt(7))]=647+(2+2+2)=647+6=653 is prime AND 647-6=641 is prime.

MAPLE

filter:= proc(p) local L, t, d;

  if not isprime(p) then return false fi;

  L:= convert(p, base, 10);

  d:= add(floor(sqrt(t)), t=L);

  isprime(p-d) and isprime(p+d)

end proc:

select(filter, [seq(i, i=3..20000, 2)]); # Robert Israel, Apr 14 2020

PROG

(PARI) isok(p) = isprime(p) && (d=digits(p)) && (sd = sum(i=1, #d, sqrtint(d[i]))) && isprime(p+sd) && isprime(p-sd); \\ Michel Marcus, Jan 19 2014

CROSSREFS

Sequence in context: A185555 A093941 A072952 * A302379 A303100 A302951

Adjacent sequences:  A179631 A179632 A179633 * A179635 A179636 A179637

KEYWORD

nonn,base

AUTHOR

Carmine Suriano, Jul 21 2010

EXTENSIONS

Definition clarified by Robert Israel, Apr 14 2020

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 16 19:48 EST 2022. Contains 350376 sequences. (Running on oeis4.)