A340553 a(n) = card({k: prime(n) mod k is not prime}).

2, 3, 4, 5, 6, 9, 9, 12, 10, 16, 19, 22, 23, 24, 21, 29, 30, 38, 38, 39, 45, 47, 44, 53, 59, 57, 60, 57, 72, 67, 77, 74, 79, 86, 90, 94, 95, 97, 93, 100, 107, 119, 116, 125, 121, 130, 135, 135, 128, 150, 143, 147, 160, 156, 159, 160, 169, 174, 175, 185, 175

Offset

1,1

Links

Table of n, a(n) for n=1..61.

Example

a(9) = 10 because prime(9) = 23 and 23 mod k is only not prime for k in {1, 2, 11, 13, 14, 15, 17, 19, 22, 23}.
a(10) = 16 because prime(10) = 27 and 27 mod k is only not prime for k in {1, 2, 4, 5, 7, 10, 14, 15, 17, 19, 20, 21, 23, 25, 28, 29}.

Prog

(PARI) a(n) = my(p=prime(n)); sum(k=1, p, !isprime(p % k)); \\ Michel Marcus, Jan 21 2021

Crossrefs

Sequence in context: A075164 A240827 A023841 * A380817 A245605 A269863

Adjacent sequences: A340550 A340551 A340552 * A340554 A340555 A340556

Keyword

nonn

Author

Peter Luschny, Jan 21 2021

Status

approved