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A072963 In prime factorization of n replace all single (i.e., non-twin) primes with 1. 1
1, 1, 3, 1, 5, 3, 7, 1, 9, 5, 11, 3, 13, 7, 15, 1, 17, 9, 19, 5, 21, 11, 1, 3, 25, 13, 27, 7, 29, 15, 31, 1, 33, 17, 35, 9, 1, 19, 39, 5, 41, 21, 43, 11, 45, 1, 1, 3, 49, 25, 51, 13, 1, 27, 55, 7, 57, 29, 59, 15, 61, 31, 63, 1, 65, 33, 1, 17, 3, 35, 71, 9, 73, 1, 75, 19, 77, 39, 1, 5, 81 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(a(n)) = a(n).

LINKS

Table of n, a(n) for n=1..81.

FORMULA

Multiplicative with a(p) = (if p+2 or p-2 is prime then p else 1), p prime.

EXAMPLE

a(92) = a(2*2*23) = 1; a(93) = a(3*31) = 3*31 = 93.

CROSSREFS

Cf. A007510, A000040.

Sequence in context: A145799 A244568 A098985 * A161955 A276234 A000265

Adjacent sequences:  A072960 A072961 A072962 * A072964 A072965 A072966

KEYWORD

nonn,mult

AUTHOR

Reinhard Zumkeller, Aug 20 2002

STATUS

approved

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Last modified April 20 17:54 EDT 2019. Contains 322310 sequences. (Running on oeis4.)