Sequence of the Day (archive)

The Sequence of the Day (archive) page is in reverse chronological order of year and month. For current month, see Future (next 2 months) OEIS Wiki contributors to SoD.

November 2010

OEIS Wiki contributors for November 2010 Sequence of the Day

Date	OEIS Wiki contributor	Sequence of the Day	Comment
1	Alonso del Arte	A118372 $\scriptstyle {\mathcal {S}}\,$-perfect numbers.	Cf. Granville numbers
2	Alonso del Arte	A090232 First year in office of $\scriptstyle n\,$-th President of the United States of America.	U. S. Election Day
3	M. F. Hasler	A098516 Minimum wind speed in mph for a category $\scriptstyle n\,$ hurricane in the Saffir-Simpson hurricane scale.	Max has a draft on one of his user subpages.
4	Alonso del Arte	A001783 $\prod _{\stackrel {i=1}{(i,n)=1}}^{n}i=\prod _{i=1}^{n}i^{\delta _{1}^{(i,n)}}\,$ The "phi-torial" of $\scriptstyle n\,$.	Cf. Euler's totient function or phi(n); $\scriptstyle i\nmid n\,$ means i does not divide n (not what we want, would be wanted for "nondivisorial,") $\scriptstyle (i,n)\,\equiv \,\gcd(i,n)\,=\,1\,$ (what we want for "phitorial" or "coprimorial.")
5	Alonso del Arte	A001567 Fermat pseudoprimes to base 2. (Sarrus numbers or Poulet Numbers)	Cf. Fermat pseudoprimes
6	Alonso del Arte	A083216 Fibonacci-like primefree sequence.
7	Alonso del Arte	A018226 Magic numbers.
8	Alonso del Arte	A002372 Number of decompositions of 2$\scriptstyle n\,$ into ordered sums of two odd primes.	Cf. Goldbach conjecture
9	Alonso del Arte	A001491 Opus numbers of Beethoven's 9 Symphonies.
10	Alonso del Arte	A059999 $\scriptstyle {\frac {1}{6}}n^{5}-{\frac {19}{8}}n^{4}+{\frac {51}{4}}n^{3}-{\frac {253}{8}}n^{2}+{\frac {445}{12}}n-14,\ n\,\geq \,1.\,$	{2, 3, 5, 7, 11, 42, ...} Wiggles through the first 5 primes, then gives up... Since a polynomial of degree k can be fitted to wiggle through k+1 points, a polynomial of degree 5 could be fitted to wiggle through primes 2, 3, 5, 7, 11, 13.
11	Alonso del Arte	A053664 Smallest number $\scriptstyle m\,$ such that $\scriptstyle m\,\equiv \,i{\pmod {p_{i}}}\,$ for $\scriptstyle 1\,\leq \,i\,\leq \,n.\,$	Cf. Chinese remainder theorem | Veterans' Day.
12	Daniel Forgues	A024702 $\scriptstyle a(n)\,=\,{\frac {(p^{2}-1)}{24}}\,$, where $\scriptstyle p\,$ = prime$\scriptstyle (n+2),\ n\,\geq \,1.$	Subsequence of generalized pentagonal numbers (Cf. A001318.) Major changes to http://oeis.org/ as of today: http://oeis.org/classic moved to http://oeis.org/ Sequence pages moved to http://oeis.org/ only (no more on http://oeis.org/wiki/) Please use: {{oeis|A??????}}: A?????? which is more convenient and flexible than [[OEIS: A??????]]: OEIS: A?????? or [[OEIS: A??????|A??????]]: A?????? instead of [[A??????]]: A??????.
13	Alonso del Arte	A175607 Largest number $\scriptstyle x\,$ such that the greatest prime factor of $\scriptstyle x^{2}-1\,$ is $\scriptstyle p_{n}\,$.	Proof that there is such a largest $\scriptstyle x\,$ for each prime $\scriptstyle p_{n},\ n\,\geq \,1\,$?
14	Alonso del Arte	A038770 Numbers divisible by at least one of their base 10 digits.
15	Alonso del Arte	A001468 Another version of the infinite Fibonacci word.
16	Alonso del Arte	A038699 Smallest prime of form $\scriptstyle n\,2^{m}-1\,$ or 0 if no such prime exists.
17	Alonso del Arte	A090206 Composite Fibonacci numbers (or intersection of A000045 and A002808.)
18	Alonso del Arte	A051254 Mills primes, obtained by computing $\scriptstyle \lfloor M^{3^{n}}\rfloor \,$, where $M$ is Mills' constant.
19	Alonso del Arte	A034872 Central column of Lozanić's triangle.
20	Alonso del Arte	A017354 $\scriptstyle (10n+7)^{2}\,$ (A098403 Area of Mandelbrot set.)	Related to heptagonal numbers (A000566.) Birthday of Benoit Mandelbrot. (If no one else does the write-up by 22:00, Al will choose a different sequence.)
21	Alonso del Arte	A081119 Number of integral solutions to Mordell's equation $\scriptstyle y^{2}\,=\,x^{3}+n\,$.
22	Alonso del Arte	A038772 Numbers not divisible by any of their base 10 digits.	Primes in this sequence obviously can't have any of their digits be 1.
23	Alonso del Arte	A115020 Count backwards from 100 in steps of 7.	Sometimes used to gauge the concentration ability of a patient with Alzheimer's disease.
24	Alonso del Arte	A167452 Smallest sequence which lists the position of digits "2" in the sequence.
25	Alonso del Arte	A103225 Gaussian integer equivalent to the totient function	Thanksgiving.
26	Alonso del Arte	A097545 / A097546 Farey fraction approximations to π
27	Daniel Forgues	Axxxxxx Odd spoof perfect numbers (only one term known: Descartes' 198585576189!)	Cf. A058007 Freestyle perfect numbers: perfect numbers and spoof perfect numbers.
28	Alonso del Arte	A104272 Ramanujan primes.
29	Alonso del Arte	A003052 Base 10 self numbers.
30	Alonso del Arte	A028442 Zeros of the Mertens function.

October 2010

OEIS Wiki contributors for October 2010 Sequence of the Day

Date	OEIS Wiki contributor	Sequence of the Day	Comment
1	N/A	N/A
2	N/A	N/A
3	N/A	N/A
4	N/A	N/A
5	N/A	N/A
6	N/A	N/A
7	N/A	N/A
8	N/A	N/A
9	N/A	N/A
10	Alonso del Arte	A020988 (2/3)*(4^n-1).	Birthday of Sequence of the Day and birthday of Neil Sloane.
11	Alonso del Arte	A005820 3-perfect (triply perfect, tri-perfect, triperfect or sous-double) numbers: sum of divisors of n is 3n.
12	Daniel Forgues	A092291 Let p = n-th irregular prime, A000928(n). Then a(n) = smallest value of m such that numerator(Bernoulli(2*m)/(2*m)) / numerator(Bernoulli(2*m)/(2*m*(2*m-1))) equals p.
13	Jaume Oliver Lafont	A006720 Somos-4 sequence: a(0)=a(1)=a(2)=a(3)=1; for n >= 4, a(n)=(a(n-1)a(n-3)+a(n-2)^2)/a(n-4).
14	Maximilian Hasler	A057652 Numbers n such that n-2^k is a lucky number for all k such that 1 < 2^k < n.
15	Alonso del Arte	A014437 Odd Fibonacci numbers.
16	Alonso del Arte	A118130 Composite lucky numbers whose divisors are also lucky numbers.	C++ program that generates n lucky numbers in order
17	Alonso del Arte	A027884 Figaro's opening aria in 'Le Nozze di Figaro' by Mozart.
18	David W. Wilson	A020639 lpf(n): least prime dividing n (a(1) = 1).
19	Daniel Forgues	A014580 Binary irreducible polynomials (primes in ring GF(2)[ X ]), evaluated at X=2.	Carryless arithmetic base 2
20	Charles R Greathouse IV	A177854 Smallest prime of rank n.
21	T. D. Noe	A000029 Number of necklaces with n beads of 2 colors, allowing turning over.	Birthday of Martin Gardner
22	Alonso del Arte	A005349 Harshad numbers.
23	David W. Wilson	A036236 Least positive number k such that the remainder when 2^k is divided by k is n.
24	Alonso del Arte	A070308 Numbers such that the sum of each base 10 digit squared adds up to the sum of the proper divisors.
25	Alonso del Arte	A036787 Numbers requiring as many digits in base 10 as in Roman numerals.
26	Alonso del Arte	A080035 "Orderly" Friedman numbers (or "good" Friedman numbers): Friedman numbers (A036057) where the construction digits are used in the proper order.	Cf. Category:Nice Friedman numbers
27	Alonso del Arte	A035327 Write n in binary, interchange 0's and 1's.
28	Alonso del Arte	A006567 Base 10 emirps.
29	Alonso del Arte	A069151 Base 10 Smarandache-Wellin primes.
30	Alonso del Arte	A030101 Convert n to binary, reverse the bits, and convert back to decimal.
31	Alonso del Arte	A008595 Multiples of 13.	Halloween.