A302049 a(n) = 1 if n = prime(k)*prime(1+k) for some k, otherwise 0.

0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Offset

1,1

Comments

Characteristic function for products of 2 successive primes (A006094).

Links

Antti Karttunen, Table of n, a(n) for n = 1..67591

Index entries for characteristic functions

Index entries for sequences computed from indices in prime factorization

Formula

a(n) = A137794(n) * A280710(n).

a(n) = A185013(A246277(n)) = A185013(A078898(n)).

Prog

(PARI) A302049(n) = if(n<=1, 0, my(p=precprime(sqrtint(n))); p>1 && 0==(n%p) && isprime(n/p) && (nextprime(p+1)==n/p)); \\ After code in A006094
(PARI) first(n) = my(res = vector(n), p = 2); forprime(q = 3, , if(p * q > n, return(res)); res[p * q]++; p = q) \\ David A. Corneth, Apr 24 2018

Crossrefs

Cf. A006094, A078898, A137794, A246277, A280710, A302047, A302048.

Sequence in context: A318880 A177063 A341619 * A373383 A078926 A324824

Adjacent sequences: A302046 A302047 A302048 * A302050 A302051 A302052

Keyword

nonn

Author

Antti Karttunen, Apr 24 2018

Status

approved