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A165198 Primes from integers by taking the factorial of each digit and adding them up. 0
2, 2, 2, 3, 7, 3, 3, 7, 7, 3, 3, 3, 3, 5, 13, 31, 127, 727, 31, 127, 241, 727, 45361, 45361, 5, 5, 5, 5, 13, 31, 127, 727, 13, 31, 127, 727, 13, 13, 31, 31, 127, 127, 727, 727, 31, 31, 31, 31, 127, 241, 127, 241, 127, 127, 241, 241, 727, 727, 727, 727, 45361, 45361, 45361 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The integers are considered in increasing order.

All primes eventually appear. Least integer k which produces the n-th prime: 2, 12, 122, 13, 1223, 133, 12233, 1333, 122333, 1224, 134, 1334, 122334, 13334, 1223334, ..., . - Robert G. Wilson v, Sep 30 2009

LINKS

Table of n, a(n) for n=1..63.

Dario Alpern, Factorization using the Elliptic Curve Method

EXAMPLE

2 from 11 by 1! + 1!.

3 from 100 by 1! + 0! + 0!

13 from 133 by 1! + 3! + 3!

727 from 136 by 1! + 3! + 6!

45361 from 178 by 1! + 7! + 8!

155->241. 178->45361. 1223->11. 1224->29. 1333->19. 1334->37. 1336->733. 1345->151. - R. J. Mathar, Sep 17 2009

MATHEMATICA

f[n_] := Plus @@ (IntegerDigits@ n!); k = 0; lst = {}; While[k < 783, a = f@k; If[ PrimeQ@a, AppendTo[lst, a]]; k++ ]; lst (* Robert G. Wilson v, Sep 30 2009 *)

CROSSREFS

Cf. A061602. - R. J. Mathar, Sep 17 2009

Sequence in context: A091712 A125721 A049798 * A245526 A024682 A091228

Adjacent sequences:  A165195 A165196 A165197 * A165199 A165200 A165201

KEYWORD

base,nonn

AUTHOR

Parthasarathy Nambi, Sep 07 2009

EXTENSIONS

2! = 2 and 10 -> 1! + 0! = 2 prepended by R. J. Mathar, Sep 17 2009

STATUS

approved

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Last modified October 16 21:10 EDT 2019. Contains 328103 sequences. (Running on oeis4.)