A141219 Write the n-th nonprime (A018252(n)) as a product of primes; increase one copy of the largest prime by 1 and decrease one copy of the smallest prime by 1, multiply the resulting numbers.

1, 3, 4, 6, 8, 6, 8, 8, 12, 12, 12, 12, 16, 12, 16, 24, 14, 24, 16, 18, 24, 24, 18, 32, 24, 20, 28, 24, 24, 24, 36, 24, 32, 48, 30, 36, 28, 36, 48, 32, 40, 30, 36, 32, 48, 48, 56, 36, 36, 48, 40, 48, 38, 60, 40, 72, 42, 48, 72, 42, 48, 72, 44, 60, 48, 54, 84

Offset

1,2

Links

Table of n, a(n) for n=1..67.

Example

1st nonprime = 1 (has no prime factors); a(1) = empty product = 1.
2nd nonprime = 4 = (p(max)=2)*(p(min)=2); a(2) = (2+1)*(2-1) = 3*1 = 3.
3rd nonprime = 6 = (p(max)=3)*(p(min)=2); a(3) = (3+1)*(2-1) = 4*1 = 4.
4th nonprime = 8 = (p(max)=2)*(p=2)*(p(min)=2); a(4) = (2+1)*2*(2-1) = 3*2*1 = 6.

Crossrefs

Sequence in context: A290115 A225794 A206769 * A069211 A368152 A242822

Adjacent sequences: A141216 A141217 A141218 * A141220 A141221 A141222

Keyword

nonn

Author

Juri-Stepan Gerasimov, Aug 07 2008

Extensions

Three terms corrected by R. J. Mathar, Aug 18 2008

Entry revised by Jon E. Schoenfield, Mar 09 2014, following revision of A141218 by N. J. A. Sloane

Status

approved