# Smarandache–Wellin number

(Redirected from Smarandache-Wellin prime)

In mathematics, a Smarandache–Wellin number is an integer that in a given base is the concatenation of the first n prime numbers written in that base. Smarandache–Wellin numbers are named after Florentin Smarandache and Paul R. Wellin.

The first decimal Smarandache–Wellin numbers are:

2, 23, 235, 2357, 235711, 23571113, 2357111317, 235711131719, 23571113171923, 2357111317192329, ... (sequence A019518 in the OEIS).

## Smarandache–Wellin prime

A Smarandache–Wellin number that is also prime is called a Smarandache–Wellin prime. The first three are 2, 23 and 2357 (sequence A069151 in the OEIS). The fourth has 355 digits and ends with the digits 719.[1]

The primes at the end of the concatenation in the Smarandache–Wellin primes are

2, 3, 7, 719, 1033, 2297, 3037, 11927, ... (sequence A046284 in the OEIS).

The indices of the Smarandache–Wellin primes in the sequence of Smarandache–Wellin numbers are:

1, 2, 4, 128, 174, 342, 435, 1429, ... (sequence A046035 in the OEIS).

The 1429th Smarandache–Wellin number is a probable prime with 5719 digits ending in 11927, discovered by Eric W. Weisstein in 1998.[2] If it is proven prime, it will be the eighth Smarandache–Wellin prime. In March 2009 Weisstein's search showed the index of the next Smarandache–Wellin prime (if one exists) is at least 22077.[3]

## Smarandache number

The Smarandache numbers are the concatenation of the numbers 1 to n. That is:

1, 12, 123, 1234, 12345, 123456, 1234567, 12345678, 123456789, 12345678910, 1234567891011, 123456789101112, 12345678910111213, 1234567891011121314, 123456789101112131415, ... (sequence A007908 in the OEIS)

## Smarandache prime

A Smarandache prime is a Smarandache number that is also prime. However, all of the first 200000 Smarandache numbers are not prime. It is conjectured there are infinitely many Smarandache primes, but none are known as of November 2015.[4]

## Factorization of Smarandache numbers

 n Factorization of Sm(n) n Factorization of Sm(n) 1 1 16 22 × 2507191691 × 1231026625769 2 22 × 3 17 32 × 47 × 4993 × 584538396786764503 3 3 × 41 18 2 × 32 × 97 × 88241 × 801309546900123763 4 2 × 617 19 13 × 43 × 79 × 281 × 1193 × 833929457045867563 5 3 × 5 × 823 20 25 × 3 × 5 × 323339 × 3347983 × 2375923237887317 6 26 × 3 × 643 21 3 × 17 × 37 × 43 × 103 × 131 × 140453 × 802851238177109689 7 127 × 9721 22 2 × 7 × 1427 × 3169 × 85829 × 2271991367799686681549 8 2 × 32 × 47 × 14593 23 3 × 41 × 769 × 13052194181136110820214375991629 9 32 × 3607 × 3803 24 22 × 3 × 7 × 978770977394515241 × 1501601205715706321 10 2 × 5 × 1234567891 25 52 × 15461 × 31309647077 × 1020138683879280489689401 11 3 × 7 × 13 × 67 × 107 × 630803 26 2 × 34 × 21347 × 2345807 × 982658598563 × 154870313069150249 12 23 × 3 × 2437 × 2110805449 27 33 × 192 × 4547 × 68891 × 40434918154163992944412000742833 13 113 × 125693 × 869211457 28 23 × 47 × 409 × 416603295903037 × 192699737522238137890605091 14 2 × 3 × 205761315168520219 29 3 × 859 × 24526282862310130729 × 19532994432886141889218213 15 3 × 5 × 8230452606740808761 30 2 × 3 × 5 × 13 × 49269439 × 370677592383442753 × 17333107067824345178861

## Generalization

Since there are no known original Smarandache primes, there are three generalizations of them to find some related primes.

• Least k such that concatenating k consecutive natural numbers beginning with n is prime are
?, 1, 1, 4, 1, 2, 1, 2, 179, ?, 1, 2, 1, 4, 5, 28, 1, 3590, 1, 4, ?, ?, 1, ?, 25, 122, ?, 46, 1, ?, 1, ?, 71, 4, 569, 2, 1, 20, 5, ?, 1, 2, 1, 8, ?, ?, 1, ?, 193, 2, ?, ?, 1, ?, ?, 2, 5, 4, 1, ?, 1, 2, ?, 4, ... (sequence A244424 in the OEIS)
• Least k such that the number formed by concatenating the decimal numbers 1, 2, 3, ..., k, but omitting n is prime are
2, 3, 7, 9, 11, 7, 11, 1873, 19, 14513, 13, 961, ?, 653, ?, 5109, 493, 757, 29, 1313, ... (sequence A262300 in the OEIS)
• Least k such that concatenation of first k numbers in base n is prime are
2, 15, 2, ?, 2, 11, 10, 3, 2, ?, 2, 5, ?, 3, 2, 13, 2, ?, ?, 3, 2, ?, 9, 7, ?, ?, 2, ?, 2, 7, ?, 3, 5, 25, 2, 323, 226, 3, 2, ?, 2, 5, ?, 3, 2, 31, 85, 7, ?, ?, 2, ?, 14, 5, ?, 3, 2, ?, 2, ?, ?, 15, 10, ?, ...