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A305894 Filter sequence for a(Sophie Germain primes) = constant sequences. 1
1, 2, 2, 3, 2, 4, 5, 6, 7, 8, 2, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 2, 20, 21, 22, 23, 24, 2, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 2, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 2, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 2, 76, 77, 78, 79, 80, 2, 81 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For all i, j:

  a(i) = a(j) => A305800(i) = A305800(j),

  a(i) = a(j) => A305978(i) = A305978(j).

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..100000

FORMULA

a(1) = 1; for n > 1, a(n) = 2 if A156660(n) == 1 [when n is in A005384 = 2, 3, 5, 11, 23, 29, 41, 53, 83, 89, 113, ...], otherwise a(n) = 1+n-A156874(n).

PROG

(PARI)

up_to = 100000;

A156660(n) = (isprime(n)&&isprime(2*n+1)); \\ From A156660

partialsums(f, up_to) = { my(v = vector(up_to), s=0); for(i=1, up_to, s += f(i); v[i] = s); (v); }

v156874 = partialsums(A156660, up_to);

A156874(n) = v156874[n];

A305894(n) = if(n<2, n, if(A156660(n), 2, 1+n-A156874(n)));

CROSSREFS

Cf. A005384, A156660, A156874, A305800, A305810, A305978.

Sequence in context: A305978 A305985 A319706 * A305811 A239471 A241509

Adjacent sequences:  A305891 A305892 A305893 * A305895 A305896 A305897

KEYWORD

nonn

AUTHOR

Antti Karttunen, Jul 01 2018

STATUS

approved

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Last modified September 21 17:46 EDT 2019. Contains 327273 sequences. (Running on oeis4.)