A129145 -id:A129145 - cp's OEIS frontend

A129146 a(n) = n-th odd prime minus n-th odd composite number.

-6, -10, -14, -14, -14, -16, -16, -16, -16, -18, -14, -14, -14, -16, -12, -10, -14, -10, -10, -12, -8, -8, -4, 2, 2, -2, -4, -6, -4, 8, 10, 14, 14, 20, 18, 22, 22, 24, 28, 32, 28, 36, 34, 36, 34, 42, 52, 52, 52, 50, 54, 54, 62, 62, 62, 66, 66, 70, 72, 70, 78, 90, 92, 92, 92, 100, 102, 110, 106, 108, 112, 118, 120, 124, 124, 128

Offset: 1

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Zak Seidov, Apr 01 2007

sign
easy

For small n's, a(n) is negative, while for large n's, a(n) is positive.

Cf. A065091, A071904, A129131, A129145.

from sympy import primepi, prime
def A129146(n):
    if n == 1: return -6
    m, k = n, primepi(n) + n + (n>>1)
    while m != k:
        m, k = k, primepi(k) + n + (k>>1)
    return prime(n+1)-m # Chai Wah Wu, Aug 01 2024

a(n) = A065091(n) - A071904(n).

cp's OEIS Frontend

A129146 a(n) = n-th odd prime minus n-th odd composite number.

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