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A177149 Indices n such that the sums of the squares of the digits of prime(n) are prime. 1
5, 9, 13, 18, 23, 26, 30, 32, 33, 40, 41, 43, 45, 46, 48, 50, 64, 65, 66, 67, 68, 71, 74, 75, 78, 79, 80, 86, 87, 89, 90, 91, 110, 116, 117, 118, 121, 124, 128, 130, 131, 137, 139, 145, 150, 153, 156, 157, 159, 164, 165, 167, 168, 170, 171, 173, 174, 182, 184, 185 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

n such that prime(n) is in A108662. - Robert Israel, Aug 05 2019

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

5 is in the sequence because the 5th prime is 11, and 1^2 + 1^2 = 2 prime;

9 is in the sequence because the 9th prime is 23, and 2^2 + 3^2 = 13 prime;

139 is in the sequence because the 139th prime is 797, and 7^2 + 9^2 + 7^2 =179 prime.

MAPLE

with(numtheory): nn:= 150: T:=array(1..nn):k:=1:for n from 1 to 731 do:p:=ithprime(n):l:=evalf(floor(ilog10(p))+1):n0:=p:s:=0:for m from 1 to l do:q:=n0:u:=irem(q, 10):v:=iquo(q, 10):n0:=v :s:=s+u^2:od:if type(s, prime)=true then T[k]:=n:k:=k+1: else fi:od:print(T):

# Simpler:

filter:= proc(n) isprime(add(t^2, t=convert(ithprime(n), base, 10))) end proc:

select(filter, [$1..1000]); # Robert Israel, Aug 05 2019

CROSSREFS

Cf. A108662.

Sequence in context: A314716 A314717 A314718 * A301291 A314719 A314720

Adjacent sequences:  A177146 A177147 A177148 * A177150 A177151 A177152

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, May 03 2010

STATUS

approved

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Last modified February 28 01:15 EST 2020. Contains 332319 sequences. (Running on oeis4.)