A267144 Octagonal numbers with prime indices.

8, 21, 65, 133, 341, 481, 833, 1045, 1541, 2465, 2821, 4033, 4961, 5461, 6533, 8321, 10325, 11041, 13333, 14981, 15841, 18565, 20501, 23585, 28033, 30401, 31621, 34133, 35425, 38081, 48133, 51221, 56033, 57685, 66305, 68101, 73633, 79381, 83333, 89441, 95765

Offset

1,1

Links

Table of n, a(n) for n=1..41.

Eric Weisstein's World of Mathematics, Octagonal Number

Eric Weisstein's World of Mathematics, Prime Number

Formula

a(n) = prime(n)*(3*prime(n) - 2) = A000040(n)*(3*A000040(n) - 2).

a(n) = A000567(A000040(n)).

a(n) = sigma_0(24^(prime(n) - 1)) = A000005(A009968(A000040(n) - 1)).

Mathematica

Table[Prime[n] (3 Prime[n] - 2), {n, 1, 45}]

Prog

(PARI) lista(nn) = forprime(p=2, nn, print1(p*(3*p-2), ", ")); \\ Altug Alkan, Jan 11 2016
(Magma) [NthPrime(n)*(3*NthPrime(n)-2): n in [1..50]]; // Vincenzo Librandi, Jan 12 2016
(Python)
from sympy import prime
def a(n): p = prime(n); return p*(3*p-2)
print([a(n) for n in range(1, 42)]) # Michael S. Branicky, Aug 21 2021

Crossrefs

Cf. A000040, A000567, A001248, A034953, A116995, A117961.

Sequence in context: A096018 A381179 A297647 * A240516 A079386 A156304

Adjacent sequences: A267141 A267142 A267143 * A267145 A267146 A267147

Keyword

nonn,easy

Author

Ilya Gutkovskiy, Jan 11 2016

Status

approved