A303263 Indices of primes in tribonacci sequence A000073.

4, 6, 7, 11, 87, 98, 215, 802, 4202, 18699, 96879

Offset

1,1

Comments

T = A000073 is defined by T(n+1) = T(n) + T(n-1) + T(n-2), T(2) = 1, T(1) = T(0) = 0.

The largest terms correspond to unproven probable primes T(a(n)).

Links

Table of n, a(n) for n=1..11.

Formula

a(n) = A092835(n) + 1 = index of A092836(n) in A000073.

Mathematica

-1 + Position[LinearRecurrence[{1, 1, 1}, {0, 0, 1}, 10^4], _?PrimeQ][[All, 1]] (* Michael De Vlieger, Apr 21 2018 *)

Prog

(PARI) a(n, N=4, S=vector(N, i, i>N-2))={for(i=N, oo, ispseudoprime(S[i%N+1]=2*S[(i-1)%N+1]-S[i%N+1])&&!n--&&return(i))}

Crossrefs

Cf. A000073 (= T), A092836 (= T(a(n))), A092835 (= a(n) - 1).

Cf. A001605 (indices of primes in Fibonacci numbers A000045).

Sequence in context: A102132 A102143 A364725 * A056853 A024566 A166457

Adjacent sequences: A303260 A303261 A303262 * A303264 A303265 A303266

Keyword

nonn,hard,more

Author

M. F. Hasler, Apr 18 2018

Status

approved