A133155 - OEIS

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A133155

Numbers formed by setting bits representing odd primes, where bit_no = (prime - 1)/2. Setting bit number b is the same as OR-ing with 2^b (i.e., bit numbers start at zero).

2, 6, 14, 46, 110, 366, 878, 2926, 19310, 52078, 314222, 1362798, 3459950, 11848558, 78957422, 615828334, 1689570158, 10279504750, 44639243118, 113358719854, 663114533742, 2862137789294, 20454323833710, 301929300544366, 1427829207386990, 3679629021072238

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..26.

FORMULA

a(n) = setbit(a(n-1),(p-1)/2) where p is the n-th odd prime.

EXAMPLE

a(3) = 14 because 3, 5 and 7 are odd primes so therefore bits 1, 2 and 3 are set and bit zero is not. 1110_2 = 14.

PROG

#!/usr/bin/python import gmpy a = gmpy.mpz(0) i = 0 for p in range(3, 100, 2): if gmpy.is_prime(p): a = gmpy.setbit(a, (p-1)/2) i += 1 print i, a

CROSSREFS