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A338821 Primes prime(k) such that A338820(k) is prime. 3
23, 53, 73, 139, 277, 281, 283, 307, 313, 347, 359, 383, 449, 571, 733, 751, 947, 1013, 1049, 1129, 1151, 1259, 1381, 1559, 1621, 1693, 1973, 2087, 2089, 2111, 2251, 2477, 2539, 2579, 2593, 2693, 2801, 2803, 2917, 3001, 3121, 3217, 3373, 3511, 3617, 3797, 4013, 4261, 4463, 4549, 4567, 4639, 4643 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Primes p such that the sum of (q^2 mod p) for primes q < p is prime.

LINKS

Robert Israel, Table of n, a(n) for n = 1..3700

EXAMPLE

a(3) = 73 because it is prime and (2^2 mod 73) + (3^2 mod 73) + (5^2 mod 73) + ... + (71^2 mod 73) = 661 is prime. 73 = prime(21) where A338820(21) = 661, and this is the third prime value in A338820.

MAPLE

N:= 1000: # for terms in the first N primes

P:= [seq(ithprime(i), i=1..N)]:

R:= NULL:

for n from 1 to N do

v:= add(P[i]^2 mod P[n], i=1..n-1);

   if isprime(v) then R:= R, P[n] fi

od:

R;

CROSSREFS

Cf. A338102, A338820.

Sequence in context: A113912 A327920 A055782 * A104802 A128473 A132235

Adjacent sequences:  A338818 A338819 A338820 * A338822 A338823 A338824

KEYWORD

nonn

AUTHOR

J. M. Bergot and Robert Israel, Nov 10 2020

STATUS

approved

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Last modified December 5 12:24 EST 2021. Contains 349557 sequences. (Running on oeis4.)